I gotta agree on the filter and bad gas. My truck sat for a year at a shop- and ran like garbage after I finally got it back, stalling, hesitating, running lean, etc. Turns out- little brown bits of gunk was pulled into the filter from the tank. I replaced the filter, and later had to replace the fuel pump since it had sucked up all that junk. That, and burning several tanks of fuel to dilute and get rid of the old gas I couldn't siphon out took care of the problem.