on Tuesday 11 September 2007 07:15 pm, someone posing as pkup83 took a rock and etched into the cave:
You didn't say how many miles are on the truck. However, I'd suggest the following to check:
EGR Valve O2 Sensors (there are two, AFAIK) Fuel Injectors
This is what I remember being the weak parts of the 4.3L engine. There may be more but that's what I remember. The vacumn leak may or may not even be an issue.