[Mike C]

For a 35 mile trip, you will be fine anywhere under 3000 rpm. Bigger tires can drop the rpm more for you, but if you are serious about driving it any distance at freeway speeds, then either an OD trans or a set of 3.73 would be wise investment.

Once again, assuming you have the Dana rear. The Eaton rear the 4.10 gear is the lowest GM installed. I think it was Randy's Ring and Pinion had some 3.90 made years ago but they were big bucks.

If you can fab, a semi-float 14 bolt would be a great swap and fairly easy to find with 3.73 gears in a Suburban. (I put a 4.10 SF 14 in the back of my Jimmy.)