With oem 29 in tall stock gy runflats that right but if you put tires on that are 1/2 shorter or taller the rpm will be off about 100 rpm either way. Thats really not that bad i remember with my 68 roadrunner i had 4.10 gears with a 4 speed and at 80 i was tacking 4200 rpm.
The srt8 auto tranny 5th gear ratio is 0.83 and with the lx cars the gear ratio is 3.06,jeeps 3.73 and lx 5th gear overall ratio is 2.54 and the jeep 3.10. At 80 mph the lx cars are tacking 2350 rpm and the jeeps 3000.
Swapping transmissions isn't going to do much of anything, unless you're adding more gears. The Jeep has 3.73 gears in the front and rear diffs. If you can find gears for our unique front diff, you might be able to swap to the LX gear ratio, but your Jeep will be slow off the line with less gear.