96 3500 454 running very rough

have just bought a 96 3500 454 from a guy for 250.00. trucks in great shape except that it runs rough and sometime hardly at all. the guy put on new fuel pump, cap, rotor, plugs and plug wires. it always seems to idle great, but when working its best it seems to bog after shifting (manual tranny) and can never put it to the floor without "cutting out". When working its worst it will idle good but the second you give it ANY gas it wants to die. So if anyone has any ideas please give a suggestion.
worst case is i take my 250 dollar truck to the chevy dealership and have them fix it and im still money ahead, but if i can save a buck i dont mind doing that either!

Thanks in advance for any help

Sounds like it may possibly be starving for fuel. I don't see anything in your post about the guy replacing the fuel filter or cleaning the injectors. That would be the next step i would think. Replace the fuel filter and pour some injector cleaner into the tank.

Have you checked the vacuum hoses for any splits, cracks, or holes? If that doesn't do it, when does it run good? (hot, cold, downhill, etc); when does it run the worst?

Thanks for the advise guys.

I bought a fuel pressure gage and it read 50lbs. but when i gave it gas it dropped to 40-45 and i could see the pressure drop when it started to run bad so i did change the fuel filter and it made a difference. It still went to 50 but only dropped a couple of lbs when i gave it gas. I would say that took care of 85% of the problem. It still does it a little under HEAVY accelaration. I think i read in a post on a different problem that the 454 should be at 60lbs when turning the key to the on position, so i think this weekend ill take off the top of the intake manifold and try to make a regulator adjustment, Ill post the results.

Once again thanks for the advise guys!