More likely the converter check valve got a speck of dirt in it and didn't seal, letting the fluid drain back. It won't refill the converter in park. Put the selector in neutral for a bit, while it's idling, and it will refill.712edf said:Back in the day (70s) folks would use type F in 727's to get firmer shifts. It was essentially the same as using "trick shift" fluids.
I once put ATF+3 in a 85 D350 to top it off. When I went to drive it 4 days later it wouldn't move. I pulled the 727 & had it rebuilt. The transmission guy said there was only normal wear & no reason for it to not move, that my converter must have went bad. Coincidence? Maybe but I never bought ATF=3 again.
Bucky