99 PONT GRAND PRIX GT, "TRANSMISSION"

I HAD RECENTLY REPLACED THE TRANSMISSION GASKET WHICH I THINK I TIGHTENED DOWN TO MUCH WHICH IN TURN HAS NOW CREATED A SMALL LEAK. THIS WILL HAVE TO BE REPLACED AGAIN BUT I FOUND OUT THAT YOU ONLY TIGHTEN DOWN UNTIL YOU "START" TO SEE THE GASKET BULGE OUT.I DID REPLACE THE FLUID THAT I LOST WHEN DROPPING THE PAN.I ALSO PUT IN TOO MUCH FLUID (APROX A PINT AND A HALF TOO MUCH). IT WAS ABOVE THE MAX MARK ON THE STICK ABOUT AN INCH. IT RAN LIKE THAT FOR ABOUT 2MONTHS, THIS PAST WEEK I DRAINED A PINT AND A HALF OUT AND NOW ITS WITHIN THE LIMIT MARKS ON THE STICK WHEN IDLING IN PARK.***** WILL OVER FILLING HAVE ANYTHING TO DO WITH THE FOLLOWING 2 PROBLEMS I HAVE JUST NOTICED ON MY DAUGHTER'S CAR OR IS IT AN ADJUSTMENT OF THE BANDS??
PROBLEMS:
#1 UPON STARTING ACCELLERATION, THERE IS A SMALL SLIP, ALMOST UNMENTIONABLE BUT COULD BE THE START OF SOMETHING AND IT IS CONSISTANT.IT'S BEEN GOING ON FOR THE PAST MONTH. IT DOESN'T HAPPEN AT THE START OF 2ND,3RD OR WHEN GOING INTO 4TH GEAR.
#2 WHEN IN 4TH GEAR AT ABOUT 50 MPH, AND I DECIDE TO COAST I NOTICED THE RPM NEEDLE DROPS QUICKLY ABOUT 1500 RPMS AND THEN WILL RISE QUICKLY WHEN YOU GO TO ACCELLERATE TO THE SAME RPM THAT YOU LEFT OFF AT IN WHICH IT ENGAGES THE TRANSMISSION AGAIN.THIS DOESN'T HAPPEN WITH ANY OF THE OTHER GEARS. IS THIS SLIPPAGE? CAN THIS BE ADJUSTED? I'M TRYING TO GRASP WHAT THE CAUSE MAY BE AND WHAT THE EXPECTED COST MAY BE WHEN I BRING IT IN. THANK YOU FOR ANY AND ALL INPUT YOU MAY HAVE. LARRY.