I was right abnout the three fingered grip

Says pro Bob Hilborn

4. Take Pinky off Racquet
With three fingers and a thumb on the racquet, the player won’t grip the racquet as tight. This will allow the player to swing more freely. When you first attempt this, you’ll feel as if the racquet might fly out of your hand. This is certainly not the case but does prove how tight you’ve been holding the racquet in the past.

That discovery made sense,  I should have done a search.  But try the grip on  all your stokes for one practice.  If it works for serving then it should work for ground strokes.

I should mention.  Those three fingers and thumb have control, which the pinkie did not.  I hold the three finger, western grip and play that with both fore and backhand.  It works great, all the way from the service box on  my first try with the wall.  Those fingers are very accurate, they can make minute, tiny changes in the racket impact poiny, a very fine tuning of the stroke timing.

And a trick I just learned on my living room wall.  When I need the power boost,, I just squeeze that pinkie back on  the grip..

Who else uses those fingers? Basketball players, they roll the ball off of them, and they provide the final element of precision.  Those joints combined make an articulated pendulum, a swinging joint which can be fine tuned in rotation.