2013 GMC Sierra 1500 Intermittent Hard Shifting Issue

I have a 2013 GMC Sierra. It started having an intermittent shifting issue about a year ago - right after I paid it off!

It's always had a bit of a clunk to it when downshifting, but that eventually turned into a much bigger issue. It started shifting HARD out of park, in reverse, in the lower gears, and sometimes in the higher gears. At one point, while going uphill and trying to shift, it shuddered and almost cut off on me - and trust me, I was not straining it. Another time it randomly cut off at a red light. Sometimes it cranks slowly. The sifting issue has gotten progressively worse, but weirdly, it comes and goes! Sometimes I'll go a week without issue at all (shifting down or up) and it will shift beautifully for a while, then it'll suddenly (seemingly at random) go back to shifting hard in every gear (especially in the lower ones and reverse). Notably, there have been a few times after a hard rain that the issue returned after not doing it for a while, but not after EVERY rain.

About 8-months ago, I took it to mechanic shop #1. After three trips back and forth to this same mechanic with no luck, down the road it went to mechanic shop #2. My poor transmission has been in and out probably six times. They've gone over the wiring again and again. It really does seem like an electrical problem due to its intermittence. I'm at the point of probably having to go find a new vehicle, because I can't keep pouring money into fixing this one. I love this truck, and I don't make a lot of money, so I'm super upset/stressed about it.

Here is what various mechanics have done that has somehow not fixed the issue:

• wiring harness replacement (twice)

• all solenoids replaced (twice)

• TCM replacement (once)

• Mass airflow sensor (twice)

• valve body (twice)

• battery (once)

• transmission servicing

I've researched and wonder now if the transmission range sensor could be the issue, but heck if I know! Any ideas or suggestions would be appreciated because I am at a loss.