gsr swap sputtering

Hey guys, i have a gsr swap in my coupe...everything is running fine but not too long ago i went to the track and ever since then it sputters...Ill be driving and around 3000 rpms it starts to not pick up like if it was misfiring...but if i give it some throttle itll go...i know a couple of people that this is happening to and noone can find out what the problem is..hopeflly somebodys had this before and can help out...thanks