You nailed that one on the head. No reputable shop is going to put their name on the line in a small town for a little stinkin transmission.

 

I am having the same problem! I am not trying to hijack thread just inform all of what I have done to no avail...

Changed gov pressure switch and solenoid; No Better
complete flush and filter; No better
changed PCM had performance PCM in and put stock back in; No Better
Bit the bullet and put in a rebuilt, upgraded tranny (better clutches etc...) all sensors came with "new" tranny; No Better

At this point I am at a loss... all of the above suggestions have been tried, so pointing away from tranny problem, have read a little about a check valve in the line but have not done anything about that yet...

 

I have a 2000 durango with the 5.9. 4x4. Love my truck. It has 150,000 miles on it and runs like a champ. Last week I drove home and the next morning I left for work and it wouldn't shift past 1st gear. I took it home parked it. Checked fluid,was fine. Everything looked ok. Called Mechanic to come look at it. He said tranny was shot. 1800.00 estimate on rebuilt tranny.
so.......... I did some research and found a few speed sensorsensor on the tranny. I went and spent 20 bucks and bought the rear speed sensor. Took it home and 5 minutes later bam. My truck was back to running top notch. If u have problems with yours not shifting past 1st. I suggest do what I did. Speed sensor. Easy fix. Located on bottom side of tranny. Hope this helps somebody save some money