[sector95]

The "MIL" is the Malfunction Indicator Light aka Check Engine light. It really doesn't *do* anything but indicates your engine management computer has logged a malfunction code. To find out what the code is, you need to access the engine computer and download the code (with the help of an expensive little gizmo). This is what the mechanics will usually do first to get them pointed in the right direction.

If this were my truck, I'd bite the bullet and have it taken to either the dealer or a good independent shop. From your troubleshooting, it seems as if the engine is not getting fuel. My first reaction would have been the same; replace the fuel filter. I would suspect your fuel pump is not putting out enough pressure to fire the injectors. The fact this condition changed gradually over time would lead me to suspect the pump. There's another post on this board... it's new so it's near the top of the list... about this same sort of situation. The fuel pump checked okay for pressure at idle, but couldn't provide enough pressure to run the engine otherwise. I would replace the fuel pump and see if doesn't clear up the situation and if not, time to cry "uncle" and let the "pros" have a crack at it. I believe you have a more sophisticated fuel injection system than the regular 4.3L throttle body system. In short, there are special tools needed to fully troubleshoot a fuel injection system and there may be some other components involved (possibly a fuel shutoff relay or something else along those lines) that only a trained mechanic should be able to check.

Good luck...

Mike