1992 HELP sunbird unusual stalling

My parents have a 92 sunbird that will stall if driven for more than half an hour or at high speed. It will start in neutral and park, but when put in any gear, the car dies. If it sits for a while, it will then run normally. 4 cyl, not sure which. Started about 6 months ago. No GM tech or any other mechanic can figure this out. The car will always start, runs fine, and is in imaculate cond. Just turned 100,000 kms. Everything on this car works. Best answer we have been given was " If the car does it again, just let it sit for a little while.... heres your money back." Again, it ALWAYS starts. Put it in drive or reverse, it dies. I do know about the safety features of the car. Like if the battery is flat, once the brake is deployed, the car will stall. We have had the sensors checked and replaced. When the car stalls while driving, it just dies, no sputter. We were told that the coil or something in the distributer was overheating, but we have replaced most components to date. If you have heard of this happening your information would be greatly appreciated. Thanks.

Sounds like a ignition issue to me.