Is your truck a 1/2, 3/4, or 1 ton? If it is a 4spd on the floor, even if you regear, I doubt you will use first unless you're hauling a load of hay up a hill or something. Your trans might be the SM420 I think which has a first gear of 7.something crazy low gear. But sure, I think you can regear the rear you have. Check Jim Carter's truck parts from the ads on this site. They sell all different ratios. If your truck is a 1 ton, you might have a 5.14 rear like mine.
