Dying 93 sable

I have had car about a year. I have changed motor and tranny. I replaced coil with msd coil. Remanufactured fuel injectors and distributor. New spark plugs, wires, cap and rotor. I have changed the ignition control module. new throttle position sensor. The car will run for different amounts of time each time then it will die and take a will to start. sometimes it will run for awhile before doing it other times it will take awhile to start back up at all. I have changer fuel filter and air filter too. I would greatly appreciate any thoughts on the subject.