A 13 vane rotor upgrade is fine ,But they are selective.If it isnt the appropriate thickness to correspond with the pump pocket depth you can lose as much as 60 psi. max line pressure hot.This could cause shift concerns and or slipping at medium to heavy throttle.Kevlar band is a looser in the 2004R transmission and causes long drawn out shifts.Apressure test shopuld be performaed and if it is good I suggest installing our shift recalibration kit.