The real issue with the 3.92 and other trucks is stock is that FCA nerfed the throttle response curse SO BAD. 2/3 of the pedal is dead.
A pedal commander while only remapping the throttle response REALLY made my truck driveable. I'm completely amazed at how much of a difference it makes. Coming from a PHEV that had a sport mode that did similar thrings with the throttle mapping and suspension when set to sport mode, it was easier for me to accept and not just attribute the anemic feeling my truck had overall to turbo lag. It is practically gone with the pedal commander.
FWIW the 3.21 should give you better highway mileage. the 3.92 is geared more for towing, so the 8th gear is shorter giving more torque and a higher rpm at highway speed. the 3.21 should be about 20% better. the rest of the transmission 2nd through 7th are the same. 7th is 3.92 on the 3.21 and 8th is 3.21. the 3.92 has a lower 1st gear, then its all the same as the 3.21. the 3.92 is marginally quicker due to shorter gears. but its fractions of a second.
for me, the pedal commander took my truck from going 0-60 in about 7-9 seconds to a sub 5 second if I can keep traction control from kicking in spinning the 285r22 tires. A stab of the gas in town and I can usually chirp the tires in 2wd. before it was just a delay and slow response. going up an onramp to 70mph no longe feels like a slog, the truck is happily going 70mph even pulling 4,000lbs as fast as I need it to.
This nannying BS is going to get people killed. The throttle should be responsive and predictable not a mush pile of lag to meet some BS emissions mark so some chukclefark at FCA can get a bonus. Same with the IBS Shenanigans.