I had same problem. Was corrosion on a circuit board connector just below the shift lever. Cleaning it did nothing for me, so likely a chip or resistor burned out.
I replaced with new shift selector assembly and was around $240. Came with a new shift cable, which is easy to attach to trans lever. I see one on eBay now for $118. If you buy used, get closeup photos of the connector on right rear corner as you look down at it. A lot of people have had the same issue with water.
That connector is a little tricky and could have not been engaged all the way. Try that first. It’s one where you have to push down a tab that is hard to see and swing away a lever to release. Pins are tiny, so be careful that it’s engaged. The mechanic could have bent some pins during reassembly.
to get there, you need to remove center console. Might take you an hour or two....pretty easy really.
Good luck!

Now that I think about it, you can check the connector and I think you can even pull the whole assembly also without removing the console. Just pull the shifter surround. There were four 10mm bolts holding the plastic shifter assembly to the body. Getting the connector off is easier if you remove those bolts as the assembly can rotate to give you better access to the connector retaining clip.

Check with Abran (user here). He often has spares....

I haven’t came across any other people with the same symptoms as you, so not sure. I did just read a post (here, I think) about a dealer adjusting a “T bar” from underneath that allowed truck to go into sport mode, so it could be mechanical.

I was able to pull the board to look at it, it wasn’t too hard to figure out. Couple of screws and it slid out, if I recall correctly.
The assembly is 4 10mm bolts. Since I bought new, the shifting felt like a new truck and was worth the money to me.
Doubt if the cable is difficult to remove, but you may need to adjust from underneath if the cable is a little different length.

good luck!