GM wouldn’t start offering hybrids in its vehicles until 2004 with its GMT800 platformed pickups. The first was the Chevy Silverado Hybrid.
Compared to hybrids today, the hybrid system in the truck was simple and extremely mild. Rather than having a full blown hybrid system with a battery, the system consisted of an electric motor inside the transmission flywheel. This essentially acted as a starter/start/stop system/alternator for the engine, powering accessories and the truck’s battery. When coming to a complete stop, the engine would shut off, but then the electric motor used 48V power to restart the engine. Three 14V batteries under the rear seats provided a bit of extra power that were charged by regenerative braking.
There was no assist mode nor could the system move the trucks on electricity alone. Any fuel economy gains the trucks received were entirely from its ability to start and stop the engine. Those gains were modest. Some saw a 10 percent increase as the system was still linked to a big 5.3 liter V8. Others, like Motor Trend in their long term test, didn’t see the value as they only saw a 1-1.5 mpg improvement over the standard engine. And it wasn’t cheap; while the hybrid option was $1,500, it required pricey option packages: a Silverado extended cab 4X4 with an auto started at just over $31,000. After adding the hybrid and its other pricey but required packages, you wound up with a near $40,000 mild hybrid pickup in 2004 dollars.