Your favorite car mod for mpg??

[bandit86]

I have a 01 beetle diesel. Needs a 6th gear revs too high. There is a overdrive gear conversion for $500 but I'd rather get taller skinny tires.

My 03 dodge ram diesel loves the 35" tires, nice low rpm with 6speed and 373 gears, I often look for 7th. I dream that if anything happens to that truck I would put the engine and trans into a newer dodge with the 3.23 gears.