Fuel problems with 88Z24

I am having some fuel problems with my 88 Z24. I have done a lot of work to this car and I am usually good at diagnosing problems, but this one really escapes me. The fuel charcoal canister would occasionally leak fuel out of it's air valve. The car will jerk badly when I try to maintain speed. What is weird is that when I disconnect the Purge Control Valve, the car will run awesome, but If i plug it back in, the vapor canister blows out fuel and the car jerks. Fuel pressure checks out ok. What can I do?! I really love this car and I have spent a lot of money on it to keep it in tip top shape. Please help. Below is a list of fuel related items that I have replaced.

Fuel Pump, fuel pump relay, fuel pressure regulator, fuel injectors, charcoal canister, purge control valve, fuel filter, fuel lines.

This may sound stupid but try loosening your gas cap and trying it. I had a Tahoe do this to me last year.

Tried loosening the gas cap, but that didn't help. I leave the gas cap loose anyway just to prevent pressure from building up in the tank. When the purge control vavle is disconnected, the only route from the tank to the engine is the lines that feed the fuel rail. As a result, pressure would build up in the tank until it collapsed in on itself if the gas cap was tight. Any other suggestions would be greatly appreciated.