Allison 1000 (6-Speed) Automatic
Type
Automatic
Speeds
6
Years
2006-2019
Builder
Allison Transmission
Paired with: Chevrolet/GMC 2500HD-3500, Duramax LBZ, LMM, LML, and early L5P
Simplified torque-flow diagram — where this transmission sits in the drivetrain, not a literal cutaway of its internals.
A 2005-introduced "Generation 4" revision of the Allison 1000 that added a sixth, double-overdrive gear and higher torque capacity, arriving with the LBZ Duramax and continuing through the LMM, LML, and the first three model years of the L5P before GM moved to a 10-speed unit for 2020.
Strengths
- Meaningfully higher torque capacity than the earlier 5-speed generation, matching the growing output of later Duramax engines.
- A genuine commercial-truck-grade automatic, carrying forward the core reputation of the Allison 1000 family for durability under heavy use.
Known weaknesses
Shares several Allison 1000-family issues with the earlier 5-speed generation, including C3 clutch pack lubrication and torque converter lockup surge complaints.
Note: See the 5-speed Allison 1000 profile for the shared failure modes; the same category of fixes generally applies.
Still has a real, if higher, capacity ceiling before internal upgrades become necessary under significant added power.
Note: Budget for internal upgrades on any build meaningfully above stock output.
Sources
- Allison 1000 transmission (Wikipedia) (accessed 2026-09-22)
- Allison 5 & 6 Speed Transmission, Problems, Solutions & Upgrades (NextGen Diesel) (accessed 2026-09-22)
- Weak Links Of The Allison (Diesel World Magazine) (accessed 2026-09-22)