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2005 Chevy Silverado 3500 Duramax - Allison 1000 Rebuild

Upgrading GM's Strongest Transmission For Extreme Use

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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.

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.

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.

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.

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.

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