As a counterpoint: my truck lives in 8th gear (literally). I bet 95% of its life is 8th gear, and yes that includes many hours of "rolling terrain". I'm also on 20 inch rims (stock diameter though).
Downshifting is not some boogyman either, it's a seamless 400 rpm increase and if you have tunes on or you're talking in a conversion its completely unnoticeable. The point of having all these gears, is to use them at times likes this. The truck always has a gear that makes the most sense, who cares if it drops a gear? That's why you have 8 of them.
And don't forget, when you're in the city: the 3.92 usually creates 1 extra upshift/downshift vs the 3.21, it uses more gears to get to the same speed. So if you're THAT concerned about shifting, then be honest and mention that the 3.92 is definitely more busy in the city.
Pick your poison.
For me, nothing better than cruising on the freeway at 1400 to 1500 RPMs for hours at a time, the truck is just idling its way through life with minimal drama.
Though I absolutely agree that the time for the 3.21 is when you're buying the truck, probably too late at this point unless the truck is brand new and you plan to drive the wheels off it.
Edit: ok I just realized you have the 3.6 with the 3.21. Completely different story, I know nothing about how that drive train feels. The hemi/3.21 is glorious though, no complaints. The OP drives a hemi, not the 3.6.