I have a 2000 bonneville ssei, and today as i was coming home from work my car starting shifting hard. I got the car home and checked the transmission fluid and everything was fine. It has done this one time before but this time was a lot harder shift. please help!!!!!!!!!!!!!!

Does the hard shifting occur on up shifts only? Does it only happen after you've been driving a while? If so, I would say it sounds like the Pressure Control Solenoid. Do a search for it and you'll find out all you need to. If you get the car scanned and get a code P1811 then you'll know for sure. Otherwise I'm guessing it could be a tranny mount. When I had this problem I had to replace both items.

thanks so much, I am going to get that checked. I'll let you know what happened. My car does exactly the same as you described. only shifted hard on upshifts. downshifts are fine. I am going to check. thanks again.

Easy fix.. Check your front tire pressure. Mine does this anytime one get 3 -4 lbs lower than the other. Just got back from a 2000 mile trip and it about drove me nuts one day, checked the pressure and one was low.

My friend who owns a trans shop and a few GM'* himself told me it has to do with the computer thinking the trans is slipping due to one wheel spinning more reves each mile vs th other. Sounds lke a line of bull, but every time mine does that I find a pressue diff on one of the fronts.

P.*. If you turn the key off for a minute and back on it will reset for a while then do it again if it is a tire.

now everything is fine with my car. I went to my mechanic and did transmission oil change and now everything with my car is fine. I also changed spark plugs and wires(which the old ones were really crappy because the wires broke). But thanks for all the help from you guys.
THANKS AGAIN TO EVERYONE FOR THERE INPUT!!!!!!!!!!!!!!!!!