88 Gmc C2500 Misfire Question

[88 GMC Truck]

I just installed a new EGR Valve because I was having a misfire at startup and also throughout the power range(Slightly though). Because I have a new engine and intake with a TBI 2BBL I was unable to get an EGR number from the old EGR Valve and the new EGR Valve has eleven washers ranging in different inside diamitors. I selected a washer in the middle and now when the truck starts and warms up, I still have the miss from cold to warm up and I now have a very bad pre-ignition knock. My question is this - after replacing an EGR valve can the washer size have a detrimental effect on the ignition causing a bad knock or could it be a knock sensor causing the miss and also the pre ignition detonation? Thanks in advance! BTW All the other electronic components in the engine compartment have been replaced with new and this also includes a new eprom chip and computer.