My '89 Mustang will stall after 15-20 minutes, once it’s warm. (It’s completely stock and has always run perfectly.) It doesn't matter if I'm driving it or not - it stalls sitting in the driveway, going 70MPH down the highway (giving it gas) and while sitting at a light (revving or not as I've tried both). Both the battery gauge needle and the tach suddenly fall to zero and it shuts off, sometimes those two gauges will drop like it’s going to stall but the engine will kick back up and keep running. But once it starts stalling, it become more and more difficult to restart. It never did this until the Mustang shop I bring it to, did some tuning, replaced the EGR sensor and adjusted my idle, leading me to believe that it is an electrical problem, maybe the work they did uncovered a problem? (The thing is, is that they keep telling me they can’t get the car to reproduce the problem - it does it without fail for me every time I drive it. So either they can’t figure it out or they just don’t want to spend the time on it. I feel like I’ve been thrown out into the cold!) I've also had the following recently replaced: alternator, voltage regulator, battery, battery cables, starter. It's not the fuel pump as I can hear this every time I start the car. And if it is a fuel problem, why doesn't it occur instantly? Why wait until the car is warm? Maybe a vacuum leak?? I am completely frustrated. I would really appreciate any suggestions!!!!