My son is now the proud owner of my old 89 Chevy 2500 4X4. It has a TH400 and a 350, which have both been rebuilt. It has ~ 80k on it and has always ran very strong with zero problems... Until recently. A couple of weeks ago he called and told me his truck was running very poorly and that it had run fine the day before. It started out looking like a fuel problem but no so sure now. I can get it to run and idle fair IF I unplug the MAP sensor. If unplug the MAP and put it into gear, it will die. BUT, if I leave the MAP unplugged (Vacuum line only) AND disconnect the TPS, it will continue to idle once I put it in gear. I have replaced/inspected so far: Fuel filter TPS sensor IAC Distributor(complete including rotor and cap) MAP sensor tested (I may have diagnosed incorrectly, however) Plugs and wires EGR is working As noted, I can get it to run smoothly in park if I unhook the vacuum to the MAP but if I put it in gear it will bog down and die. AND, if I unplug the MAP AND disconnect the TPS, I can put it in gear and it will continue to run. To the point I am pretty sure that I could drive it. But if I plug either of them back in, it will die. I could use any input on this one. Thanks in advance.