It doesn't matter if you're a Chevy, Dodge, or Ford owner, the Allison transmission brand is a name known throughout the industry for strength and durability.
In stock form, the Allison 1000 is rated to handle up to 365 hp and 660 lb-ft of torque in 1-ton GM pickups. Those are impressive numbers, to be sure, but it's not enough capacity to survive behind the fire-breathing, twin-everything Duramax engines that guys are building now. Even the mighty Allison 1000 has its limits.
When a truck comes into Inglewood Transmission with a problem, the first thing Mike Lovrich does is plug in his General Motors Tech 2 scan tool and read the trouble codes. This step is critical for modern electronic transmissions, and it told us the Allison 1000 we brought in had two codes stored: P0731 (First gear transmission slip) and P0746 (electronic pressure-control solenoid problem). Both codes were cleared, and the truck was put on the lift. | 
The Allison 1000 weighs approximately 360 pounds, so rather than risk damaging a case by dropping it, Inglewood used the mother of all specialty tools-a transmission jack/workstation that bolted directly to the PTO access hole on the side of the transmission. | 
Inglewood Transmission technicians unhooked both batteries before unplugging a single connector or removing a single bolt. The importance of the electronic side of these transmissions can't be stressed enough. |
Typically, the Allison has proved to be good for around 80 hp and 160 lb-ft more than stock before durability becomes an issue. Those numbers aren't carved in stone, though, and drivers who tow or haul extreme loads may find their Allison isn't up to the task-even at power levels that many would consider mild.
Inside the shop, the transmission fluid was drained into a bucket and the teardown began by removing the torque converter and unbolting the bellhousing from the main case. | 
The transmission pump was then unbolted from the bellhousing. We saw evidence that the fluid was burned up pretty badly, but there were no signs of big broken metal pieces. | 
The Allison's input shaft and clutch drum were pulled out of the main case and placed on the bench to drain the old ATF out of them. |
That's exactly where Maurice Rozo of Off Road Unlimited found himself. His '05 Silverado 3500 was optioned out and modified to serve double duty as a daily driver and a trailer-towing, off-road beast. The truck underwent major chassis upgrades to convert the front suspension to a solid axle and clear 37-inch tires. The engine remained relatively stock, except for a Hypertech programmer and a TTS Power Systems after-cat exhaust. We'll bring you a full feature on the truck at a later date, but for now, all you need to keep in mind is that this Chevy has very mild power upgrades but wiped out its Allison because it weighs 9,600 pounds (including driver). And that's before it even hooks up to a trailer.
The snap rings holding in the C1 and C2 clutch plates were removed, and the input shaft was pulled out of the clutch drum. | 
The C2 clutches looked fine. | 
Here's where the problem was. When the technicians tried to remove the C1 backing plate, they found out the clutch plates were seized to the hub. |
Cutting back the power or making the truck lighter weren't options for Rozo, but when the transmission began slipping at 17,000 miles and went into limp mode 100 miles later, he knew his Allison needed some upgrades.
The C1 clutch plates were destroyed. Lovrich said this type of damage can occur when the tires go from having very little traction to having very good traction with the engine at full power. This could happen when doing a burnout at the dragstrip or driving in and out of mud with lots of throttle. | 
Here's a good C1 clutch (right) next to one of the burned C1 clutches and steels. | 
The C3 clutches were pulled out next. They were burned up on their inner edges, which Lovrich says is common in these transmissions (he claims this is due to lack of lubrication). In fact, Lovrich is working on a bolt-on fix to cure this failure permanently. |
We contacted Mike Lovrich at Inglewood Transmission in Inglewood, California, and gave him the details of Rozo's truck. "No problem," Lovrich said. He told us he could have the transmission out of the truck, rebuild it with a Sun Coast Pro-Loc torque converter and rebuild kit, throw in a Transgo Shift Kit, and road test the new transmission in a day. He even let us come down and photograph the whole process.
Lovrich has developed a number of different parts and techniques for upgrading the Allison for heavy-duty use. Over the years, he's worked with the biggest names in diesel performance who have pushed him to build stronger transmissions. Thankfully, he's also worked with the biggest names in performance transmissions, so he's been able to draw on decades of experience and technology from fellow gearheads. Lovrich is one of those guys who have forgotten more about transmissions than the rest of us will ever know, yet he is still humble and knows there are still things he can learn. We knew when we showed up at his shop and he was driving his own high-powered Duramax truck that we had come to the right place.