oil pressure & transmission on 1990 Ford Bronco

i have a new oil pump&oil sending unit i drive for about 15 min oil pressure drops between 5 to 10 psi what else need to be replaced? may transmisson runs fine fwd /rev but backing up one time transmission fluid came back up out the dip stick.

Asked by for the 1990 Ford Bronco
As the oil heats up it gets thinner and pressure will be lower as the oil gets hot and about the transmission are you sure it wasn't overfull?
no it wasnt even full it was a half quart low i checked 2 day before it happen.