Transmission? Relay? Solenoid? Computer? What?

My check engine was on. Knew to check
transmission fluid because it came on around
60,000 miles and was low. Added to the max
line and it went off. Haven't had a problem
since, until today at 60,435 miles. Fluid was
still at max fill on a hot check. I decided to
drive to store. When I put it in drive, it jumped
forward. I put it in park. I repeated the process
with same result. Felt weird. Not excessive but
not normal smooth motion. Decided to
continue anyways. Gave the car gas and pulled
off but it didn't move much. I realized this as I
drove off the edge of my driveway down hill. I
stopped. I reversed without issue. I went back
to drive and pressed the gas. Nothing. Car
barely inched forward and the engine did not
rev. Reversed back to top of parking pad, up
hill, and tried on the concrete. Same results.
No rpms, no real movement. Same results in
manual mode also. Removed negative battery
cable for 10 minutes and then put it back on.
Check engine light went off and drive works
now. Drove 100+ miles today without incident.
What could be the issue?