I have a 2004 pontiac grand prix gtp. just replaced the battery and alternater. battery is dead again. its as though something is left on maybe a short somewhere? Where do I start to maybe find the problem. I made sure everything was turned off.

If you have heated seats then there is a likelihood that they are not turning off and can be difficult to tell or not when you get in the car and the sun has already been on the seat.
When they do not shut off when the motor is not running they draw enough power to drain a battery over night.
My 02 GTP had this problem and as a matter of fact it got hot enough to start burning me so I pulled the fuse. It is a 15amp fuse located in the glove box compartment, the diagram for it's location is on the inside of the fusebox cover.