ScottZLT1

I just put on a Macperformance 2 1/2inch y-pipe and new high flow cat and under drive pullies. Now when I get on the gas the car gets to 60 and starts stuttering and won't go any faster, but when you drive normal and don't accelerate fast the car gets up to 35 40 and the engine sounds like it drops in rpm. Also awhile back i put on a 52mm throttle body.Do you think that the car is getting to much air? I have no clue what this could be. if anyone has any idea what this could be or if i should just try going back to the old throttle body please tell me. i will be most humble if you can sovle this problem.