I would always recommend if you're actually questioning/considering "3.21 or 3.92" to go with more gear and get the 3.92.
I've always heard fuel difference is minor advantage to 3.21 on highway, minor advantage 3.92 in city.
I've never heard anyone seriously regretting going with 3.92, much less paying to swap down to 3.21..
3.92 better if you're ever going to get heavier, larger, wider tires
3.92 better if you're going to lift/level
3.92 better if you are going to tow
3.92 a little more effortless off the line
3.92 a little less downshifting
I also think, 3.92 will have a little more "engine braking" when downshifting up to a stop, which saves brake wear.
I have a durango RT (3.09 i think) with 32" Falken AT3W. It does fine, but definitely notice when i switch back to stock tires every winter. It also downshifts out of 8th much more frequently than my truck, and the truck has much worse aero, is heavier, and has 33s (soon to be 34s with a little lift).
3.92 in the truck is noticeable how much closer the lower gears are when accelerating