I have had my truck for about 4 years and this an ongoing problem that I cannot figure out so any help would be great. 99 qcsb 4x4 197k. I have replaced all the solenoids in the trans, the gov pressure twice with borg warner units. I have adjusted the bands, replaced the rear speed sensor and adjusted the tv cable about 30 times. My truck will not shift into third unless I let off it. Today the outside temp got above 80 and after driving the truck for 20 minutes on the interstate, it started shifting into third. Stopped for 20 minutes and it still shifted. I then parked it for about 2 hours and back to not shifting. I am thinking leaking throttle valve and would need to either replace the valve body or replaced the throttle valve. Any help or insight would be great. Thanks!

 

Update. Got the trans rebuilt and they found the 3rd gear drum seal was leaking which was causing the no shift.