For people with smog, check your vacuum check valves.
I have been having problems with my EGR valve for several weeks. Had to replace it cause it was defective. Living in california and their smog rules etc...
Well, the truck started to run like crap again. Thought I had that fixed, but it was just the old EGR going bad I guess.
Anyway did some looking at the system, and there is a vacuum check valve on the line that goes to the EGR valve, from another vacumm source, besides the ported vacuum on the carb. A little tiny thing plugged inside the vacuum line. It was letting vacuum through both ways. It's not supposed to do that. Since the check valve was bad, it was letting too much vacuum to the EGR and causing the truck to run crappy.
The Part is called a Vacuume hose check valve, part # on the valve was a D9AE-AA it was Blue and black. This valve is used from 1979 to 1995.
This valve is also used for distributor, EGR and other vacuum assisted devices.
If you have been having problems with your truck and you can't tell what's wrong or where the problem lies, don't overlook the small things like that vacuum check valve, if you have one.