Im stumped I have a 99 Durango with the 5.9. Recently I pulled away from a stop sign and it wouldn't shift out of first gear without reaching 3500-4000 rpm. The next day I jumped in it and it shifted fine until it warmed up then it went back to revving high. Downshifting works fine, fluid is clean and full. I had codes checked and revealed nothing. This trans has never slipped, shuttered or anything. Just a sudden issue that arose. I could use ANY advice you have to give.

 

My o2 sensors in another vehicle of mine did the EXACT same thing, just a thought

 

I would drop the pan and fill with licensed synthetic atf+4, my preference is the valvoline, and do a filter change and band adjustment. You could also check the tv cable.