I’d be much obliged if someone can shed light on this for me. Here’s the details of the issue I’m having

2001 F-250 lariat extended cab 4 wheel drive 4r100 transmission.

Was finishing up some college courses at the end of the semester in diesel technology. After discussing working on my own diesel truck with the instructor on our classes slow days I brought it into the shop with a slew of small jobs and tune ups to perform over the next couple days.

Started Ed with a coupe injectors and running some scans on it to get all stored codes. Then moved onto the transmission fluid and filter change.

While underneath I noticed the transmission had a rebuilt tag but that’s all I could make out on it. Proceeded with draining the pan and removing the filter. The fluid looked to be in good condition. Filter was looked normal and the magnet didn’t have no excessive fragments.

Proceeded to to put the new filter in place did even remove the old o-ring seal on old filter neck. Filled back up to specs.

I finished to trick up up at this point and figured I’d drive it home. Everything was working good. Almost home and about 45 mins into my drive the truck shifted into 3rd gear and wouldn’t shift back into overdrive. At this time the overdrive off light began to flash. A burning smell was coming from under the truck. I crippled it on ahead home and let everything cool down.

I drained the pan again and removed it. To my surprise the filter was laying inside the pan. I tried to replace it but it fell
off in my hand. I went and bought a new filter and more fluid as this fluid was burnt badly.

Done another filter and fluid change. This however did not fix the overdrive issue. The light still would flash if driven without the button pressed to turn off overdrive. It would never try shifting. Took it back to college and pulled the codes. Computer read the input turbine shaft speed sensor. Upon removing the old one and noticing it was badly melted I bought a new one. Added it and still the same problem. Only then the only code I was getting was failure to shift or something like that.

Done me a road test while hooked to the computer to get real time data. Both soliniods was shown working except during the third to fourth gear shifts.

As of today I decided to work on it some more. Went to check the fluid level and it was bone dry. There was no obvious signs of leaks. So once again got another new filter and fluid. This new filter was longer the previous two. Finished up the job and also cleaned the magnet still nothing excessive. Went for a road test and now the transmission is shifting to all four gears. However the engine RPMS are not changing when it is supposed to be in overdrive. You can feel the shift and watch the rpm gauge drop during the shift. But when exceeding speeds of 45-50 the rpms steadily rise above 2000.

I am am dumbfounded as to what this could be. If anyone has any insight please direct me on what to try next.