1995 Pontiac Firebird Hesitation, stumbling only when resta

Hello. I have a '95 Firebird that runs like a dream (100+ MPH) except when the car has been driven until it has warmed-up, shut down for 30 minutes or so then restarted. It restarts fine, but it hesitates and stumbles badly; I'm afraid I'm going to get rear-ended if I can't get the problem diagnosed. The Check Engine light does not come on. I have had the Ignition Coil and Module replaced, along with a temperature switch. I had a tune-up @ 100,000 miles, but I notice they did not replace the distributor. Before I had the coils and module replaced, I noticed a faint burning plastic odor and the mechanic said that the coils showed signs of slight melting. I can't afford to replace the car a piece at a time to locate the problem. Any direction you can provide would be appreciated. Thank you