From like 47 through 72 all the one tons have full floating rear ends. If you find a late model suburban in a junk yard that has an automatic, it probably has 4.10 gears. I have had this same problem and here's what I did:
My 59 1 ton had 5.26 gearing - so if yours has a 235 6 in there, that's probably what you have as well. That's how they got the 6 to haul a ton.
The solution is easy though. You unbolt the axles and pull them out a bit. Then unbolt the back of the differential and pull out the the case end with gears and all. (both at the bone yard and on your truck when ready to install) Then get the donor 4.10 gear set and bolt that in. Put the axles back in. Fill with oil, and you'll have a much higher top speed. I then put on the tallest 85 series truck tires I could find and that helped too. I can go 55 mph with out too much trouble.
My next project is to install a watson overdrive I recently bought, however, I am still fighting with my 47 cj2a jeep that just let go the rear engine seal. (dang it) Got to get that did first.
The gear swap is really very easy.
