Someone else who's had one go bad could probably give you a little bit more, but I would think that you should be getting codes related to the MAP sensor if it was bad. I'm going to go out on a limb and say that it's probably not fuel delivery related even though it seems like that is the most common problem around here. My main reason I say that it is because it sounds like it's running rich as hell. Your problem is probably more along the lines of a bad sensor, bad ignition part, or possibly even wiring. Did replacing the intake air temp sensor at least make it run any better? If anything your mileage should do a little better with that sensor working. At least it was probably a cheap part. If you clear the codes (remove the jumper wire while you're getting the check engine light/test light flashing), drive it around for a while and see if any more codes pop up. My TFI was bad and giving somewhat similar symptoms, but I was also getting a couple of codes related to it. Do you know how old the oxygen sensor is? I hate to tell you to throw parts at it, but those are a part that do go bad (I would say about every 80K miles) so it's not unreasonable to replace it simply for the sake of maintenance. That's something I usually replace when I do tune up work. I know that a bad o2 sensor will make it run rich, but I've never seen it so bad that it makes the vehicle underivable. Like I said in my previous post though, you may very well have a bunch of issues which are leading to the truck running like crap (fouled up oxygen sensor, clogged air filter, pcv valve gummed up, plugs and wires which need to be replaced, gummed up injectors, the list goes on and on). Maybe someone can input on where to get an oxygen sensor cheap. Good luck with your troubles.