I have a 94 chevy c3500. I just recent ly put a glass pack on it and it started to run bad. I have to hold the gas pedal to the floor until it started , even then I would have to hold it un till I began to idle smoother. When the truck is idlein it idles high around 2k rpm's I changed the o2 sensor and that doesn't seem to be helping much it did make a small difference but the motor still starts stall out but if I fether it it willl keep running. It drives well under load but it does have a high idle when I shift. I hope I gave enough info. So please help me. Thanks