Welcome to the site.
I wish I had a good answer for you but it sounds like you're possibly the most recent trans failure.
My honest guess is some damage in the torque converter or your internals are slipping so badly that they are jumping.
I would suggest the following:
Smell transmission fluid see if it smells burnt
Change the fluid & filter
Inspect the transmission pan for debris
If you find more than an 1/8" coating of fine gunk on the pan and some metal shavings on the plug or magnet then you have major problems.