Do you smell a "rotten egg/sulpher type odor" if so it would be a bad cat. converter, do you smell a smell similar to brakes dragging if so it would be a clutch lining on the disc burned out. Should be easy for any one knowledgeable with cars to give an opinion.
could be, does the engine rev high even though it' low speed? If so yes the clutch is finished, if not then the next likely thing could very well be catylitic converter is plugged, a typical symptom of a plugged cat. is an inability to accelerate relly bad gas milage and stillruns good at low speed but not under load, hope this helps