1999 Camaro spits and sputters under load

My 1999 camaro started off with a slight hesitation when climbing a hill or when I would accelerate sometimes. The Service Engine Soon light came on and when I tryed to drive it one day I could not get it to go over 15-20 mph. It spits and sputters and will not accelerate hardly at all. When I have it in Park or under no load at all, it runs fine I can rev the engine and it sounds fine. But when I go to put it under any load it just spits and sputters and coughs and won't gain any speed.I was thinking maybe the catalytic converter. But I am not sure. Any suggestions? Thank you!