I just refilled my gas tank and put in GUMOUT in it. The stuff does exactly what it says it will do. Cleans fuel injectors and cumbustion chambers and everything fuel related. I HIGHLY RECCOMEND DOING THIS EVERY ONCE IN AWHILE. My real problem is though I have heard this before but when I rev. up my engine. 4.0 HO I6 and let off the gas i hear a chopping noise. Not like metal chopping but like hiccups. I was wondering what it is I have no clue whats doing it.