I just replaced the Upper and Lower intake gaskets on my car due to coolant leaking. Once it was all back together and I started the vehicle it is running horrible. It sputters and shakes and has very little power. The car was running fine prior to changing the gaskets other than leaking the coolant and slght overheating. Any ideas why the car is now running poorly.

if the coolant was leaking into the cyl. that can foul the plugs, are there any check engine codes?

Probably misfire due to fouled plugs.

The only thing is that it was running perfect the morning before we changed out the gaskets. Then as soon as we started the car it was running really rough. Almost sounds like a it wants to stall but it wont and it has a real rough idle and take off.

ok this might help, i found a weird problem on an olds with a 3.8. Non supercharged...the pcv valve has an o-ring around the bottom to seal pcv gasses from engine vacuum. if not it will leak. its hard to explain sorry. since the pcv is on the upper intake. The olds was making a belt type squeal because crankcase pressure was so high (because it was vacuum) for instance if you took the oil cap or dipstick out it had vacuum. if you were to let it run it would stall out....that took a while to figure out!