Ok, from the provided prom ID you have a 7747 ecm running $42 mask with a BCC of AFBW. I am more familiar with ASDU and ASDX. I think replacing the injectors is a good start. Without an O2 sensor it is difficult to determine fuelling issues, but old fashioned plug reading can get you close. Your vacuum issue and timing may be the result of a non stock cam wanting timing, you may want to try and see if you can figure that out. Simply checking intake and exhaust lift will tell you if it is stock or not. Not saying that is your problem, but unknown parts make it difficult to know where to look. After replacing the injectors, please look at what the IAC is doing. The counts should be around 10 at idle and go up with throttle position and load. If the truck really wants 6 to 8 degrees of timing, it also needs to be in the bin, or it will just drop those 6 to 8 degrees out of the timing. Taking the map out of the equation means taking engine load out of the equation. You may be fighting a circular problem. Knowing that the cam is or isn't stock will help in determining why it wants timing
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