I have some thoughts but my first question is why are you running in 4th gear as opposed to 5th and a 1:1 drive ratio in the trans? I think 4th is 1.39:1 and your transfer case is is a 241? so it's 2.72:1 so your final gear reduction is ~14:1? At 400rpms your wheel speed is ~28mph?
If so, I used to run a daily driver 3rd gen that was around 775hp at the wheels with an auto 1:1 and 2.72:1 transfer and 3.73 gears at 3000-3200 rpms (~29mph) down the track.
I ran 33" tires and mud grapplers with no problems, having said that if you are running in 4th gear to stay on top of the charger, I would stick with AT.