Error code 32

I have a 1990 Chevy Astro with a 4.3, Throtte body injected. Appx. 30k on a rebuilt engine. I'm getting error code 32, saying "Vacume switch shorted to ground on start up, switch not closed after the PCM has commanded the EGR for a specified period of time or the EGR solenoid circuit is open for specified period of time. Replace the EGR valve." There is an astrisk indicating that part replacement may not fix the problem. (Consult an expert before buying replacement parts.)
I have replaced the EGR and the EGR solenoid valve. The van is still running irregularlly and I am still getting the error 32 code. I replaced the parts, now I 'm consulting the experts. What could it be?
The symptoms are. The van acts like it is running out of gas in the mid range. It will stall intermittenly. If I gun the engine it will respond immediately and run fine for a while. Then the symptoms return.