i just got my camaro back on the raod a couple days ago from putting in a 350. I notice when i pin it, it gets up pretty quick then it sounds like its over revvin then and maintains speed or slows down. but u can feel it wanting to go faster. would this be a carb issue or a spark plug issue? cuz i think they changed my spark plugs over from my 305 and 1 of them was cracked.

PS: I got a shop to put the engine incase i did something wrong.