My dad bought a white/tan 2000 Jimmy SLE 4 door 4x4 with the NP236 (the auto one) transfer case. It has about 137k miles on it and has several strange issues. First is that the engine runs strong at idle and when cold, when it warms up, it will not accelerate. I got it up to ~60 with no trouble and set the cruise, about a mile later it started to lose speed and it would not accelerate. The trans downshifted but it had absolutely NO power, it was shuddering like it had hit a rev limiter. Then it would do this at any more than about 1/4 throttle. It has a new fuel pump and the pressure is good and it ran perfect when cold.
Another problem is something produces a loud whine when the transmission is put in gear. It is a constant whine, doesn't really vary in pitch or loudness but it doesn't sound good. Fluid is red and full. Whine goes away when coasting it seems, but trans seems to shift fine.
The last apparent issue for the moment, besides the heater core supposedly, is the 4x4 does not work. The switch for the 4x4 is good, we swapped it with my '99 and it works perfect there, but in his it is completely dead. it blinks briefly when the ignition is turned on, but does not light up at all after that. The Service 4WD light is on, I thought that would be the reason but it's not. I think I heard the clicking of the front axle when driving around, which means it hasn't unlocked all the way?
I can rustle up threads for the 4x4, but I was more looking for insight to the engine and trans issues.
Thanks for the help!

**Edit to an already long post: no Service Engine light, but scanner said something weird was going on in bank 2