I had the same truck with the same issue. when the coolant temp sensor goes bad on those trucks it will run very rich and act just like you describe. It will also NOT set the check engine light. I unpluged mine and it was able to run but it then set the engine light for a coolant temp sensor curcuit fault. I guess they designed them to only monitor coolant sensor curcuit and not coolant sensor range/performance. Try unpluging the sensor(I think it is the two wire sensor to the right of the thermostat housing) if it will run on it's own after you unplug it(unplug with engine off) then you found the problem. I unpluged mine and drove it for about a week before I fixed it. It will run just a bit rich instead of pig rich like yours is now, won't hurt anything. Just remember if you do unplug the sensor you will trip the engine light and will need to clear it or disconnect the battery if it doesn't go out. Hope this helps.