Same issue on my wife's 02 GP GT: Shifts fine when cold, but after a warm up say 20 30 miles or so it shifts hard between 1&2, and really noticeable between 2&3. Had Trans back flushed at about 55,000 and now at 65,000. I hope it is something simple like a solenoid. I guess there are 2 solenoids on these: One is pressure control and the other is like an on/off switch. I am still searching for info.