If it smells like rotten eggs it is your cats, they may be clogged causing poor exhaust and partial , soon to be full, loss of power or partially clogged and burned out causing poor ecu/ 02 sensor readings. Or your 02 sensor(s) is bad cauing the engine to run overly rich and is killing the cats , chicken or the egg, egg or the chicken. It is hard to test an 02 sensor. Find out soon as the overly rich engine can cause carbon build-up