1995 Chevy Corsica no power

I believe I have 1 that will stump ya, I have a 95 corsica that when you start up in the morning runs fine but a mile down the road it loses power and I mean NO power shutters and stumbles just trying to get through a redlight. Ok heres the measures ive taken so far, ive replaced the o2 sensor fuel filter all fuel injectors the catalitic converter fuel pressure regulator, complete tune up and still nothing has changed, last week I took it to a well known repair shop and they ran a battery of test from top to bottom. Found nothing wrong with the car, the mechanic went as far to ask me if I ever found out what the problem was, would I call and let him know, he was that puzzled! After almost 3 hours and not a glimpse of what it might have been. Should I just junk the car?