I have a 1993 4wd purchased with 187k. From the beginning, I replaced all fluids, belts, plugs, plug wires, all filters. Tested milage, 16-17mpg. Then replaced, ECT and O2 sensors. No change. Did seafoam in the tank, oil, also tried lucas in the oil. I sucked 3 rounds of seafoam into the vacuum line 2 days ago to clean the carbon. Figured Cat was clogged, (need a muffler anyways), got a good 'ol boy welded me a new muffler and removed my cat yesterday. Also put in a new PCV and grommet. My truck definately has more pep, and smoother ride, and I can actually accelerate in fifth gear up a decent hill now. I have my first full tank in to check milage. Will keep posted. Anything else that yall can think of to help out?