1996 Chevy Corsica Corsica Driving Me Crazy

My corsica has the 3100 V6. The car runs like NEW. Heres the problem when I first start the car up it runs great on the 25 minute drive to work. If I work a 4-5 hour day and come out and start it up it will run FINE all the way home. When I run into a problem is. If I drive the car and let it get hot and shut it off for a short period of time (like to run into the grocery store for 10-15 minutes) and then try to start it while it is still warm/hot. It will sputter and run rough and stall out and will not staying running and then will not start. If I let it sit for 2-3 hours and get back in it. Then it will start right back up and run fine again. The check engine light comes on when it is running rough like this.I had the coils replaced because my mechanic said it was a coil pack. It seemed to run ok for about 3 weeks and started doing the same thing again. Now my mechanic is saying I should replace the igniton module.I am beginning to wonder if I am just replacing parts that he is GUESSING need replaced. Any help would be appreciated? Like I said this car runs like new for short road trips or if you let it cool off between trips. It is driving me crazy ! HELP