Tony,
The 4.3 intake plenum and combustion chambers are notorious for filling up with carbon if you don't drive them hard and run some fuel system cleaner through them every once in awhile. The Chevy dealer wants $800 for an EGR valve change and intake manifold boil out. There is also a "new" EPROM that the dealer will put in some rigs with that motor that is supposed to help out with the carbon build up. This has been a problem with our 95 Astro AWD . . . Lisa just putts around in it too much. Usually you will get a sudden drop in milage along with a code that will tell you the egr is stuck open. Heck, just go buy a new one . . . the economy could use a few folks splurging on a few new cars.
