1999 mustang GT 4R70W

The transmission has a delay to shift rom 2nd to 3rd when pushing the gas more then 30-40% or more never less. the car used to have a bad alternator and the O/D light came on with the P0782, 2-3 shift code (the alternators voltage would oscillate too high and too low in its cycle as stated by an auto parts shop employee in case its important) when I replaced the alternator it started to shift a little better and the O/D light never came back but the shift issue was...

2-3 shift problem