hi there i recently had the heads done on my 99 3.8 vt exc but it seems to lag when taking off or accelerating, but the car has plenty of compression, it has a stupid hot dog muffler (already on there) and has extractors, also when the mechanic did the heads and all that im sure the stuffed the break master, the bled the breaks but they are still non responsive (well not to a safe level anyway) wat could cause this?? please HELP