It also used a hybrid technology that would only work in the larger transmissions found in the Silverado and other large GMC trucks. That hybrid system was actually housed in the transmission cowl which unfortunately made it somewhat brittle due to the small size. Needless to say that experiment was a bust. The Voltec drive train, on the other hand, is external to the normal transmission with the batteries driving larger motors that can live outside the transmission. While each vehicle would need a specific Voltec design based on engine and transmission size, this is a much more scalable design solution and maps more directly to the changes in engine design already done based on engine and vehicle size.For the MY 2004 Chevrolet released it's first hybrid that I know of, the Silverado Hybrid. It failed. As did the second attempt, and it doesn't look good for the Three Strikes law.