National Differntial in ColoSpgs (great guys to deal with, BTW) told me a new carrier is required to go to a 3. 31. But if you only tow lightly, and have a 2wd, it may be better than a GV, et al, overdrive, giving you a similar final drive ratio.
Also, you can go higher than 2100rpm to shift, esp if you are in a bit of a hurry to get through that yellow light. :-laf I take mine up to the 3K or so governor (no tach, just guestimate) before shifting; gives me more take off pep in 3rd as well.
Daniel