mufflers or no mufflers??

the muffler shop did the exhaust system and no they did not disconnect the msd or battery. the poor performance has been there since day one. just with no mufflers and 4 ft of piping from the manifolds the car seemed way faster. once the exhuast was re-done it performed worse. the car wont rev out past 5k with the mufflers off i was able to rev to 5800 before it felt flat and that was before i paid someone to re-inspect everything i put together. after the tuning at a shop and switching out to a 8k rpm pill it revs to 6k no load but then when i drive it down the street it cuts out like the rev limiter cuts in at 5k. the shop said open the exhuast up and see if that helps. before i hack up my exhaust i want opinions on if pipe right off the manifold is a bad idea since i cannot run headers without cutting my fender well holes back open.