[MARKDTN]

12mpg is not bad. My '83 K20 used to get 14 or so with 700R4 and 3.42 gears. If you are not going to go to overdrive, I would change to 3.73 or 3.55. That should be plenty of gear for hauling and should help slightly with mileage. A more tangible benefit should be fewer RPMs at cruising speed which may be quieter inside the cab.