when i turn on my car, and just let it idle for about 15-30 minutes. Then turn it off, it will not start back up. it needs a jump to start. Now, ive gotten my battery AND alternator checked by autozone and pepboys already. They said everything was ok (well the battery has to be recharged at pepboys). i dont know what else to check for now.

 

Try this, start your car then disconnect the batt., if the car keeps running the alt. is working, to make sure it's not a problem after things warm up, let it run for "15-30 min." then disconnect the batt.
If the motor stops when you disconnect the batt. the alt. is N/G or there is a connection problem, check all the connections, from the alt. to engine bay fuse/relay box and from batt. to fuse/relay box, check batt. to chassis ground and motor/transmission to chassis ground. 94