1994 4.6 T Bird intermittantly dies but runs great when running
 

On Friday after long 4 hour drive parked then started and motor just faded. Left it till next day and got it to garage.
Changed IAC and EGR valve, took out plugged cats. Paid $701.00 and took it for a run before paying. Running best I've seen it. Went to swimming pool and she died. Called garage. They put the comp checks on it nothing shows. In other words the work they did did not help the stalling issue.
I'm majorly P'd What do we do now? They still have it. Any suggestions would be appreciated tremendously.