You might keep an eye out for a Hone Overdrive unit, probably less $$ than the gear vendors. I have one on my 75 F100, 390, 4X4, 4.10, 4 speed. Shift on the "fly" and it's a approximately a 28% gear reduction. Drops the RPM's on the highway from 3000 down to just over 2000. Really helps the MPG on the open road. I'm also going to look at a little taller tire to help stretch it out.