91 Z28, power seat..if i'm sitting in it, and i try to rock front left to rear right, it moves quite a bit...any other way it wont move, and all the bolts are tight..what could be wrong w/it?

 

Either one of the jack screws is broken or the bracket it hooks to at the top...or like mine did...both are broken..

 

what's the jack screw do?..and what bracket?..i looked under it and i didnt see nethin broke, but then again i could be wrong

 

There is a kack screw at the 4 corners of the seat and each one goes through a bracket at the top and is held there by a nut threaded on the top of the jackscrew.
To see if it is broken you'll need to remove the seat and look at the "slides" bolted to the seat bottom.