1999 Buick Regal 1999 Buick bucks or Kicks when acceleratio

Transmission problem
1999 Buick Regal 6 cyl Automatic 130000 miles

My 1999 buick regal has 130k miles now, at about 125k miles the car started to sometimes but not always buck or kick when speed hits 15 - 20 mph and again sometiimes when speed is in the 40 - 50 mph range. But once the kick happens the car runs ok at that speed and nevr happens when slowing down.

The garage I use doesn't want to replace the trans fluid as it may make matters worse.

Does this seem to indicate a new transmission is needed?