F250 3.73 to 4.30 axle ratio

Lots of guys on the Ram forum I frequent have done it and are happy. However, most recommend going with a much bigger jump than you are thinking of. 3.73 is a common ratio with the Hemi gassers and I was thinking for going to at least 4.56. If sticking with stock tires that is probably good. Guys running larger tires are doing 4.88 or 5.13. There are some good rpm calculators out there so you can see what you'd be running with the new setup.

Cost-wise the average I see is around 2K for both axles. It's varies a lot by area. Just be sure to get a good shop that specializes in differentials. It's not a project for a shade tree mechanic or weekend warrior.