My trans has an upshifting problem that just comes and goes. I have found that if I leave the fluid level at the cold full level when the trans is hot, that I have no problem. But if I fill it exactly to the full hot mark while hot, it starts to have a problem shifting into 4th.
Does anyone know what might be going on like foaming causing this?

And is it safe to run mt tranny with the fluid level a few millimeters down to the cold full level?

Thanks again everyone