WHAT CAUSES ENGINE TO STALL WHILE DRIVING

i HAVE A 1986 CHRYSLER LASER XE. IT WILL STALL WHILE RUNNING EVEN AT 40 MPH. IF I WAIT ABOUT A MINUTE IT WILL CRANK FOR A FEW TIMES, THEN RESTART. I HAVE TAKEN IT TO A SHOP AND FOUND FUEL PUMP PRESSURE IS GOOD. (THEY DID REPLACE IGNITION COIL) AFTER A DAY, IT REPEATED THE PREVIOUS SYMPTOMS. ONE CURIOUS THING THAT I FOUND BY ACCIDENT IS THAT WHEN I RUN THE A/C IT WILL NOT STALL. (I DON'T USUALLY RUN THE A/C UNLESS I HAVE PASSENGERS)I CONTACTED THE SHOP THAT WORKED ON IT BEFORE AND NOW THEY WANT TO REPLACE THE FUEL PUMP.(SEEMS STRANGE SINCE IT SUPPOSEDLY CHECKED OUT FINE)IF I WANTED TO USE THE "GUESS AND REPLACE" METHOD, I COULD HAVE DONE THAT MYSELF. ANY THOUGHTS?