Allison 6-Speed Automatic Transmission Assembly for 2016 Chevrolet & GMC
Product Notes Read before buying
This is a 6-speed Allison automatic transmission for 4WD models equipped with the 6.6L Duramax diesel engine. Fitment is confirmed for units with the transmission ID code 6AKH. Please verify this ID on your original transmission before ordering.
Voice or type your vehicle details and Wrenchy will confirm fitment in seconds.
Vehicle Fitment Guide
This part fits the following vehicles:
| SubmodelSUB- MODEL |
Body Style | Years | Engine | Attributes |
|---|---|---|---|---|
| 2016 |
| SubmodelSUB- MODEL |
Body Style | Years | Engine | Attributes |
|---|---|---|---|---|
| High Country | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| LT | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| LT | Extended Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| LT | Standard Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| LTZ | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| LTZ | Extended Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| WT | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| WT | Extended Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| WT | Standard Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| SubmodelSUB- MODEL |
Body Style | Years | Engine | Attributes |
|---|---|---|---|---|
| Base | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| Base | Extended Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| Base | Standard Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| Denali | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| SLE | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| SLE | Extended Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| SLE | Standard Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| SLT | Crew Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
| SLT | Extended Cab Pickup | 2016 | V8 6.6L DIESEL Turbo | 4WD | Automatic |
Know This Transmission Before You Buy
The research behind our purchase interview — recalls, bulletins and real install economics for this transmission family:
A quick look at your own vehicle makes sure the right transmission shows up:
- Confirm the truck has the 6.6L Duramax Diesel (LML) engine.
- Confirm the truck is a 4x4 / 4WD model.
- Check the passenger side of the transmission to ensure there is no PTO system installed.
What the install really takes — plan and budget with confidence:
Special tools this job needs:
- Heavy-duty transmission jack (minimum 500 lb capacity)
- Tall, heavy-duty jack stands
- GM transmission cooler line disconnect tools
- Professional-grade scan tool (GM Tech2, GDS2, or equivalent)
Budget for these consumables at install:
- Allison-approved TES-668 synthetic fluid (e.g., Castrol TranSynd 668) or GM-licensed Dexron VI full synthetic fluid
- Internal pan filter and pan gasket
- External spin-on fluid filter
- Front pump/input shaft seal (torque converter seal)
- Transmission cooler line flush solvent
- Replacement external spin-on filter magnet (GM Part #29535617) if original is missing
- Transmission tailhousing seal and transfer case input seal
What your vehicle’s computers will need after the swap:
What’s involved: TCM Fast Learn (Adaptive Relearn)
If reusing the original TCM, VIN reprogramming is not required, but a 'Fast Learn' adaptive pressure relearn must be performed using a professional scan tool to reset Transmission Adaptive Pressure (TAP) values. Driving without this will cause severe clutch slipping and immediate internal damage.
Pro tips for a smooth first start-up — hand them to whoever does the install:
- Torque Converter Seating: Must feel and hear three distinct clicks/drops during installation. If not fully seated, bolting the transmission to the engine will crack the pump gear and destroy the unit.
- The Lost Filter Magnet: The flat, circular magnet on top of the external spin-on filter is often accidentally discarded with the old filter. It must be transferred to the new filter.
- Post-Install Drive Cycle: After Fast Learn, perform a gentle drive learn cycle under 30% throttle through all 6 gears 25 to 30 times before heavy acceleration or towing.
- Mandatory Cooler Flush: Debris from the previous failure must be flushed from the cooler lines to prevent immediate contamination and failure of the replacement unit.
Easy to get right once you know them:
- Reusing contaminated cooler lines without flushing.
- Forcing the bellhousing bolts to pull the transmission and engine together when the torque converter is not fully seated.
- Using cheap, non-approved multi-vehicle or Dexron III fluids.
- Immediately towing or tuning the vehicle before allowing the TCM to adapt.
- Ordering a non-PTO (6AKH) unit for a commercial application that requires a PTO (6BKH) pump.
Not issues with the units on this page — the manufacturer documented these for every transmission of this family, wherever you buy one. Handy for your installer:
🔎 Recommended at install: Parts restriction by GM to investigate shift quality, slipping, or diagnostic trouble codes.
🔎 Recommended at install: Avoid heavy towing loads on aftermarket engine tunes; replace fluid or torque converter if worn.
🔎 Recommended at install: Requires complete scan tool reset and potentially internal repairs if clutches are burnt.
🔎 Recommended at install: Inspect and repair electrical pins inside the main TCM harness connector near the radiator shroud.
Researched from factory recalls, TSBs and OEM service data (reference unit 400-05265-5465125). Unit-specific details — mileage, condition, warranty, freight — are covered in the checkout interview.
Policies, in plain English.
Shipping & Handling
- Ships by LTL freight on a pallet — a real freight truck, not a parcel van
- Your checkout freight quote covers delivery to your door (liftgate service included for residential addresses)
- The carrier calls ahead to schedule a delivery window — someone must be present to receive it
- Typically palletized and picked up within 2–3 business days; transit time depends on distance
120-Day Warranty
This part includes a 120-day warranty.
- If the part fails within the warranty window, we'll replace it or refund per the coverage terms
- Coverage is parts-only — installation labor is not included
- Warranty covers defects — not installation errors, misuse, or damage after installation
Your pre-purchase interview reviews these exact terms with you before anything is charged.
Returns (30 Days)
We accept returns of uninstalled parts within 30 days of delivery for this part.
- Defective parts: We will replace the part or issue a refund at our discretion
- Programming: "Needs to be programmed to my vehicle" is not a valid return reason. Many modules require dealer programming — we're happy to help connect you with resources if your dealer says it's not programmable
- Return shipping: This part ships by freight (LTL) — the part price is refundable per the terms above, but shipping costs are non-refundable and return freight follows the seller's return terms. Your pre-purchase interview walks through the exact numbers before you buy
- Parts must be returned in original packaging and unmodified condition
- Poorly packaged returns that arrive damaged will not be credited
Damaged in Shipping?
Freight damage is rare — and you're fully protected when you do two things at delivery:
- Inspect before you sign — you're allowed time to look the pallet over while the driver waits
- Write any damage on the delivery receipt before signing — that one line is what makes a freight claim succeed
- Severe damage? Refuse the delivery — it goes back at no cost to you and we make it right
- Photograph the pallet before unwrapping; report concealed damage within 24 hours of delivery
We handle the carrier claim — you just help document it. Your pre-purchase interview walks through this checklist too.
Order Cancellation
Cancel before shipment for a full refund. Once the pallet has been built, a preparation charge may apply — and once the freight carrier picks it up, shipping costs are non-refundable and standard return terms apply. Your pre-purchase interview shows the exact numbers before you pay.
Expert Guides
2016 Sierra & Silverado 2500 HD Allison 1000 Transmission: Problems, Identification, and Used Replacement
Identify your 6AKH 6-speed Allison, understand common torque converter failures, and learn when to swap in a used OEM transmission.
Read Full Guide →Related Trouble Codes (OBD-II)
6 matching guidesIf your scan tool is showing one of these trouble codes, this part is a common fix. Each guide explains the code, how to diagnose it, and exactly what to replace.
Miscellaneous Information
OEM Part Numbers:
GMC: 24263829
Other: 6AKH
Fits Years: 2016
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This unit ships with the selling yard's 120-day warranty. Longer plans can be requested during checkout.
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