My truck had 3.42 from the factory but was wearing 33" tires when I got it and was unlocking the TCC constantly. I re geared to 4.1 but with the 33" tires that took me back to the equivalent of 3.42 on factory tire size. This works fine for what I wanted. Tire size are an integral part of the final drive ratio so make sure you take that it consideration. I also fitted an Eaton E-Locker as the factory carrier is a weakness in the 10 bolt diffs. As mine is an 1988 it also had the 28 spline axles and the Eaton only uses 32 spline so I changed my axles to Grizzly aftermarket axles. Like kennythewelder stated replace all of your bearings etc while it is all apart, no point going back later to do it all again.