A overdrive transmission would have been easier, you would have maintained the performance of the vehicle with the 3:73 rears and still have lowered your rpms while cruising down the interstate.
Brad54 hit the nail right on the head. Sometimes it's more about the quality of life than MPG. My '66 C10 has a built 350, turbo 350 and '72 1/2 ton rearend with 373 gears. I'm at the point where I can't tolerate the low rearend anymore. By the time you get where you're going your exhausted and you know the high RPMs aren't doing your engine any good. I bought a good rearend out of a '72 Suburban with 308 gears for $50 and spent another $75 to get it ready to put in the '66. Dollar wise this makes more sense than an overdrive or changing gears. I've owned several '71 and '72 1/2 ton pickups over the years with 350/350 and 308s. From my experience that's a really good all around drivetrain combo.
