1991 Ford Explorer many tranny problems come and go

My tranny is shifting too slow the fluid was burnt and overfilled so I changed it and added trick shift synthetic. When I first start out it needs some gas before it will go into gear but I think that means the fluid change caused the torque converter to leak into tranny that started after change. The slow shifting comes and goes when I first start out it shifts normally then as it heats up it shifts slower and slower but not everyday some days it is normal? Could it be a sensor or computer? Also sometimes but rarely it will feel like im in neutral when I am in drive at a stoplight on a hill it reminds me of a manual but if I give it gas it goes into gear? Because this stuff comes and goes I dont want to swap tranny if its just a sensor or something.