This has been addressed a number of times. You will probably have a ratio of 4.57 in your truck. There are direct bolt-in "pumpkins" or the complete gear assembly of the rearend from 3/4 Ton GM truck from 67 to 72, with automatic transmission, that will give you a 4.10 ratio. If you go on the Jim Carter site, he has a technical description. The only tricky part is finding one. I put one in my 1 Ton and it works really well. You can do a search for "410 gear" and you will get a lot of hits.
