You are wiser than my son. He ran his car 4.5 quarts low on fluid and claimed he checked the fluid level... Cold with the engine off!
I have not driven an automatic in years but I once had a car about 30 years ago that had a similar problem. It had a cloged filter in the transmission. One of the fellow here could advise you about that possibility.
1993 190E 2.3
2000 Toyota 4x4 Tundra