bluels-t

i got a 3in down pipe and today i had to weld it on to the stock cuz i couldnt take the smell of the exhaust anymore. when it was just 3in it ran fine, now i get on it and it stutters and carry's on, is it bad or what, dont need anything blowin up on me right now, it goes from 3inch reduced to stock ls piping..any comments or suggestions would help