The idling could be the plenum or a bad or clogged idle speed motor. I would be more concerned about the transfer case. I had a 97 ram with the shift fork and collar worn out on the transfer case. I also had to hold the shifter to get it to work, however on that one 4x4 would work but 2wd would only work if I held the shifter. That was also a worn out 3/4 ton with a pile of mileage on it so not exactly comparable to what you're looking at.