First post and wish it wasnt an issue.
I bought 2003 2500 about 7 months ago. I had the tranny serviiced and a new cooler and had a BD filter put on the PCM tohelp with TV lockuo. Sine the service it started 1-2-12 shuttle shifting. This was fixed with the solenoid and senr replace. Ever since i have no 4th, previous i did have issues where i had to let off on hte pedal and it would shift but now no 4th.
I have had it scanned wile driving and the computer is demanding 3rd as it appears to have excess voltage on the throttle signal. The APPS gives a perfect signal when powered off but not when running. Grounds have been all cleaned, battery post and connectors are shiny. The battery connectors are shiny but are original abd on the surface look their age. The batteries test at 500cca for 10 secs with hand held load tester, also no load resting volts are 12.6-7. The alternator is new and the issue is still there with alternator disconnected.
P0700 code.
Diving me nuts chasing
Truck is booked to have it reflashed next week.
?????

 

I had a similar issue with my truck- after replacing the solenoids and adding new fluid I lost 4th totally- just driving down the road I slowed down and down shifted from 4-3 and once getting back up to speed wouldn't shift back to 4. I had to have my trans rebuilt as I lost 4th/OD due to wear

 

This tranny was replaced about 150,000km ago.
I just spent a couple of hrs cleaning hardened mud from on top of the undercarriage and p8ulling plugs and contact cleaning and dielectric the sockets. I found 1 broken ground between the cab and the box. So i fired it up went for a drive and have 4th again. Not perfect shifting but at least its working.
I am still going to get the computer flashed just to ensure all updates are installed as one was for a similar issue i believe.

 

Clean your ground wire thats directly above the transmission bolted to the underside of the cab, it feeds into those sensors and can really screw things up