2007.5-2010 GMC Duramax LMM Built Transmissions

Complete Allison 1000 assemblies for the Sierra HD

Nothing else was offered behind the LMM in these pickups, so a built Allison 1000 six-speed is a like-for-like replacement with stronger internals. On a Sierra that still drives, the usual path is TCM calibration, then a billet-cover multi-disc converter, then the valve body, and a built unit only at the end. On a Sierra that is sitting with no drive, the order collapses: you buy the assembly. The practical ceiling for the stock LBZ/LMM-era unit is around 430 to 450 rwhp and 850 to 900 lb-ft, and the stock converter usually goes first, cracking its stator and ballooning its front cover. What it sheds goes everywhere the fluid goes, which is why a half repair after converter failure tends to come back.

What a built unit buys you

A built six-speed addresses the parts that limit the stock one. Billet C2 hub and billet P2 planetary for the hard three-to-four upshift that breaks them at high power. A PTO cover that routes oil to the C3 clutches, the gears where owners who tow heavy report slip and limp mode in third. Hardened pump gears and bronze bushings for the wear that makes an old Allison shift lazily and engage late. Genuine Allison solenoids rather than whatever was in the valve body at 200,000 miles. Pair that with the matched converter it ships with and the unit is working as a set instead of a collection of parts.

What we carry

BD Diesel covers the 2007.5-2010 Allison transmission and converter assembly listed here, and Calibrated Power / DuramaxTuner offers a built Allison with torque converter for the LMM. Both are complete assemblies, converter included. For engine-side work on the same truck, start from our Duramax pages.

Fitment and ordering notes

Confirm 2WD or 4WD first, because built transmissions are assembled as one or the other and the units are not the same. Core charges apply, so your old transmission is part of the deal. TCM calibration belongs in the install plan. And do not cross the 2010/2011 line shopping for a deal: 2011 Sierra HD trucks moved to the LML with a new frame, suspension and driveline, and the parts follow the truck, not the badge. We install these in our own bays in Wildwood, FL if you would rather not do it on jack stands.

Frequently asked questions

How do I know whether I need the 2WD or the 4WD unit?

Go by the truck, not the trim: if there is a transfer case behind the transmission, it is the 4WD assembly. Built units are listed separately for 2WD and 4WD because they are different builds, and an SLE, SLT or Work Truck Sierra can be either one. Give us the VIN and we will confirm it before anything ships.

Does the converter come with the transmission?

Yes on both of the complete packages here, and that is the point of buying this way. The converter is the stock Allison's weak link, so a built unit paired with a matched converter keeps one part from undoing the other. It also means the converter does not have to be sourced separately while the truck is apart.

What else should I replace while the transmission is out?

The transmission cooler lines, which leak at the factory hose-to-hardline crimp and have failed on low-mileage trucks; updated OE lines or braided lines with flared unions are the fix. Fill with Dexron-VI and use fresh filters, the TF920 sump filter or the TF950 spin-on. If you are in there with the converter off, inspect the flex plate and its bolts while you have access.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.