Paul's right.
The Porter Cable 7424 and all of the variations of this model are a tick on the weak side. Most, if not all 6.5" pads are also THICK pads.
When you use a thick pad on a Porter Cable, even on speed 6 - the energy coming out of the tool is DISIPATED by the thick foam.
This shows up your eyes as no or weak or slow pad rotation. You need that pad clipping along at a good rate of speed in order to remove defects in a timely an efficient manner.
Get a 5" backing plate and if you want to get the MOST out of this tool then get THIN foam pads.
Read the below, this is the 3rd time I've shared these two articles today.
Check out these two articles and put what they show into practice from the very start.
How to Monitor Pad Rotation? Mark Your Buffing Pads
Video: Mark your backing plate to make it easy to see pad rotation
:)