The P3AT squirms around inside a bike inner tube worse then if you had Vaseline on your hand.
Maybe a P32 doesn't kick enough to do that?
Look at Traction Grips, or Hogue, or cut your own skate-board tape.
Or get a firmer grip with exercise.
I'm 68 years old with arthritis in my hands, and can shoot a stock P3AT without it slipping until I get tired of shooting it.
rc