I think you might have found the problem: cracked vacuum hose fittings, on carbon cannister.

4.3 TBI's have a set screw, which can be adjusted to hold throttle butterflys open slightly. It is on the firewall passenger side, near throttle cable linkage, behind a metal plug, which you can drill out. I think the 2.8 tbi also has one. I set my 4.3 tbi butterflys,at lowest possible idle, with the set screw and passed Colorado emissions and drove it up Interstate 70 thru the tunnel at 11,000 feet and on out to Steamboat. This was with a broken Idle Air Control Valve, so I know you can at least keep the truck running, if you can adjust the set screw. Predrilling the plug out, at home, also gives you more possibility of performing emergency fixes, on the trail, if you need to.

I have found colored plastic tubing in all the sizes needed to replace the vacuum hoses, on my 3.1 with 4.3 TBI. The plastic will probably last longer than rubber, which cracks, when exposed to oxygen. The purple color also makes it easier to trace vaccuum hoses against black coolant hoses, fuel lines, wiring harnesses and a black engine.

Good luck [color:"blue"] [/color]