i bought my 1992 D150, 318ci MPI about a year ago, and im tired of drivin it with this problem. the truck idles fine, and runs AMAZIN when you really get into the gas. but at about mid throttle (30-55mph), the truck wants to stumble and backfire and snort out the intake, runnin REALLY rough. i replaced the TPS, thinkin maybe that was makin it run rough, no change. with more research, i found the EGR valve could be bad. ran a vacuum test on it and it is workin fine. i also replaced the spark plugs, wires, cap, and rotor. when lookin at the old cap and rotor, it looked like the rotor was hittin three of the points. when i let a mechanic drive it, he said that the bearing/bushing or distriutor plate may be loose and lettin the rotor and dist. shaft move around enuf to screw up the timin. i havent taken a look at this yet because i dont wanna pull it apart and spend more money until i know the actual problem. any suggestions? thanks