2002GPSE

Hi guys, my GPSE runs rough at about 1500 to 2000 rpm. kind of coughs a bit and sputters through the exhause. no "check engine" light. i just put in a full tune-up... however it did do this before i tuned it up. i can feel it sometimes while driving when the TCC engages. feels like a "bump" in the road but on a smooth road. do they just do that? or is there an underlying problem that sometimes doesn't set a code? any suggestions? ThanX