Just sharing all I can to possibly narrow things down.
All links expire in two days I believe. Website is called streamable and it’s a safe video hosting site. Thanks for everyone’s feedback and time on my posts.
What will you do if the transmission simply stops working tomorrow?
A remanufactured transmission from GM, Jasper or another vendor is going to run $4500 or so just for the transmission...add in $1000 for removal/reinstallation as well as fluids and fast-adapt relearn puts you at $5500.00-$6000 (maybe higher depending upon shop pricing in your area). A shop rebuild will cost a similar amount assuming they perform all the required internal updates, etc to the trans.
So unless you're in a position to drop the coin or work on the unit yourself (you've emphatically stated that's not in the cards), it really doesn't matter what's going wrong with the transmission specifically.
Here's my advice:
1) Get it to a reputable transmission shop and have it diagnosed
2) If the trans shop tells you the same thing I have and you cannot afford to repair/replace it at this time, I'd park the vehicle for now so you can list it for sale while it's still running and driving vs driving it to failure
3) Repair anything else that won't cost a lot of money but would help you sell the vehicle quicker