Dave, I didn't mean a 1:1 differential, I meant a 1:1 top gear in the transmission instead of overdrive.
The constant variable transmission like a snowmobile is a great idea and I have that rattling around in my brain too. I read about a guy who used a 17 horse Kubota in a 1200 pound car like an old triumph or something. He kept the 5 speed and clutch somehow. Around town he just left it in 3rd and got 67 mpg and 100 mpg highway. The whole theory there is it takes a much smaller engine to maintain cruise than it does to accelerate. Plus a constant engine speed is much better too.
Subaru did have it in the Justy too but I don't think there is anything like that for a pickup or larger vehicle.