The NP 231 will have 2HI, 4HI, N, 4LO. This will allow you to only use 4WD when you Need it, instead of spinning all the drivetrain all the time. With All Wheel Drive, the transfer case has to have a differential in it too, to allow for the different movement between the front and rear end when turning. ItÆs just one more thing to go wrong.

Sean

99 XJ Sport 2 Door, 4.0L, 5 speed, all stock. Daily Driver
79 F150 Standard Cab Short Box, 400ci, NP435, NP205, 35" SSRs