Feels like...A Fishtail!?!?

Here is what I have:
1999 GP GT Automatic

Here is what happens:
I go over a bump, like a pothole or manhole cover, and the back end of the car kicks out from under me. Almost like I am fishtailing. Just for a second then it goes straight.
Also, in the rain, it is SO Slippery I am scared to drive. I can barely control the thing. It has no traction.

Here is what I have had done recently:
New Tires
New Brakes
Shocks are good

Here is the Thing:
I have a magnetic tendancy for curbs...Parking lots, Sidewalks...You name it, I will scrape my tires on it.

ANY THOUGHTS??? (On my car, not my driving!)

It sounds like the rear sway bar may have broken. Jack the car up and make sure everything is properly connected. You could have broken something and I suggest that you look at everything under the back end of the car. You may want to take it to a mechanic so they can put up on a lift to see what is going on.

For a car to skate like that there has to be a problem with something in the suspension.

The last time I had a car do that, it was exactly like GTP Dad says, the sway bar busings were shot and the back end would say badly bump or no bump. Definitely get it to a shop to fix. Good luck.

:::UPDATE:::

My tires are 10 mo old. They are COMPLETELY BALD in the back! I realized this weekend that Both Rear Tires look like racing tires. Barely even signs of where the tread was. But the front two are Fine! They look really good!
I got on the TIRE section of AF and I saw a few posters have this problem.
Here are some thoughts:

Allignment
Suspension
???

So After I get the back ones replaced (Soon) I will get it up and see what the heck is going on!

Any other thoughts????