My point was, it's not the grounding that's going to jack up your mileage, it's the idle speed. You use more gas the faster the engine is spinning, therefore, when you lower rpms you're increasing fuel mileage. This is not rocket science here. Do this test; do your grounding, then adjust the throttle cable to idle your truck at 500 rpm, or whatever your's happens to idle at, then tell us if you have a mileage increase. My guess is no.
Another thing to think about is alternator output. Alts are designed to spin at a certain rate for X output. When you put something like an underdrive pulley on a car, it spins the alt slower decreasing output, which results in your headlight getting brighter when you step on the gas. I'd be interested if lowering the idle 300rpm will have this same effect.
By the way, black is the fastest color
