6 Speed Conversions

Good morning fellow calibrators I wanted to talk 6 speed conversions. My company YAK PERFORMANCE LLC has been offering a 6 speed Allison 1000 swap for some time now and I have quite a few in the wild doing what they do. The way I set my kits up depends on the budgets of the customers and how they want to put the kit together. You have some who opt for the entire kit that includes a brand new GM valve body, internal harness, TCM (W/ core or W/O core), and year specific installation parts (ex 01-03 / 04-05) while other will source their own valve bodies / TCM's and I handle the calibration update via remotely or they ship their original TCM and I bench flash/re-ship. The LB7 & LLY trucks have so much to gain from this upgrade due to the the final ratio 6th gear grants. The 0.614:1 give the truck a better operational rpm at HWY speeds as well as increased efficiency in city conditions which puts less stress on the motor and drivetrain. The one thing that sucks with any 01-04 LB7 or 04.5-05 LLY truck is going down the HWY at 80 and the truck sitting at 2250 to 2500 which creates a lot of cabin noise. This can be addressed with Dynamat to some extent but that still doesn't address all that extra engine stress which can be lowered with the .61 final ratio this in turn gives you better efficiency and increased range. I have extensively tested the 6 speed calibration on the 01-05 trucks and offer files that are tailored to each individual vehicle. This isn't a 1 file fits all, its a the customer tells me what they need and I set up the calibration to achieve their goals. If they want 3rd locked for sleds in 4wd low only they get it. If they want the best fuel economy and smoothest upshifts they get it. I take a lot of time and pride in making the best options for the best price and have a tried and true recipe for success with this platform.

In 2023 of December my company tried something a little different on a 2002 GMT800 2500HD 6.6 4x4 the original Allison finally showed signs of age on the C3 from years of service and we took the time to swap out the 01-03 original transmission with a 2011 LML Allison 1000 sourced from a local yard. Some small changes were needed but ultimately everything worked out. The newer & larger transfer case bolted up in the crossmember (Larger nuts needed) all the original drive shafts hooked up, The bellhousing had to be swapped to a 01-07 with input speed sensor bung, removal of internal mode switch, and install of original range sensor had to be addressed. Some other internal VB wiring has to be addressed but other than that a perfect fit. 2wd trucks don't have to address the newer electronic transfer case control which takes some know how but is possible. If you have a manual locking (non electronic) 4x4 this also saves you time with the transfer case install.


I really think the 6 speed conversion is a top of the list mod on the 01-05 trucks behind a lift pump, exhaust, tune being at the top of the list first. With a updated engine calibration (custom tune) you can easily push 24 to 26 mpg hwy and 18 to 20 city on the 2500 series and slightly lower with the 3500 series / Kodiak /Topkick/ trucks with the conversion like the newer trucks achieve. If anyone has any questions I'll do my best to assist. Another thing to note is the 6 speed TCM update does not affect current engine tunes you may already have. The way GM / Allison have the truck setup their systems for controlling the engine, transmission, & fuel system are standalone linked only with CAN communications for more precise operation.

Attached are some photos of the install on the 2002 2500HD Silverado