Tranny can't decide on a gear

1990 APV
Whenever I'm on the gas in gear, it continuously changes gears up and down.
If I put it to the floor, it will stay in the lower gear and go like it should.
Engine acts right when to the floor, in Park, idling at light, or putting it in neutral while going.
When it is switching back and forth between gears it cant get enough power to move much.
Basically I had to get it home by gunning it and drifting over and over.
Fluid is full and red.
Anyone have a clue? This is so much different from any tranny troubles I've seen before.
I'm wanting to blame the computer, but I really have no clue.
Thanks.

THIs trouble is not mentioned in the diagnostic chart....of course...but just in case I'd check for free movement of the throttle cable that goes to the transmission and free movement of the lever at end of cable . I suspect if it is blocked in the full throttle position, it would behave like this...