Where are the most common places for the 01 5.3 to leak? I have a po131 and po151 codes and the truck stumbles bad in closed loop. The other night when the stereo was off I could hear what sounded to be a vacuum leak under the hood. I have sprayed the whole thing down with starting fluid while running and had no increase in engine speed. I have a new fuel pump, filter, front 02's, and plugs. Have also cleaned the fuel rails. I am pretty sure it's a vac. leak. thanks for the help!!!