I have a 1990 Dodge Ram W150 with a 5.9L throttle body fuel inject system. It has started running very poorly as if the timing is changing suddenly or the fuel injection is becoming intermittent. It sounds like the timing is going to an extreme retard condition? I really don't know where to look. I did take it to a shop and they charged me a lot of money to put it on their diagnostic computer and for changing the MAP sensor and distributor cap and rotor. From what I have read online, there are conditions in the system that won't report as errors, so I'm thinking that this is one of those cases. Any ideas? For a while it was worse when the outside air temperature was cool only, but now it's pretty much all the time...

What brand of spark plugs are installed? I only recommend using the exact Champion plugs that came in the truck. If seen other plugs break down in Dodges, where the truck doesn't want to start.