Believe me, a plugged cat or precats can be a major part of most of the problems you mentioned. Eliminate those out of the equation, and then figure out what else is wrong. Plugged cats will cause a severe lack of power, poor fuel milage, funky smells, strange noises, and they certainly aren't good for engine longevity. Your car could be stalling due to the backpressure buildup... Remember Beverly Hills Cop?
