a z34 misfire?

ok i got a problem i got a 1995 monte carlo z34 i dont know that much about cars so i might sound dumb when i ask this question. but, when i drive the car it seems like it kinda sits in between first and second gear and sputters, and also white smoke come billowing out from around the catalyc converter is it a misfire or is my converter plugged hope yall can help me out