Blower max speed can be chcked by grounding the blu wire at the motor. This test by-passes the reg circuit.
If blower still does not get max rpm, then the fan should be spun by hand to see if it is free..if not, the bearings are dry..if free, then check the brushes and check the armature collector slots under the brushes..they get full of worn brush carbon and will limit rpm. They can be cleaned/cleared with a thin blade and cleaner. Also see if brushes are free to float.
If high fan w/blu jumper , then reg is bad if you have variable trigger voltage from CP at yellow wire at regulator.