1995 GMC Suburban rough idle, missing and hard start

350TBI reman motor. W/20k mil. Heads on the reman motor were junk went bad after only 20k. They were replaced w/ edelbrock performer heads#60859. The motor also has a mild edelbrock cam # 3702, edelbrock intake # 3704, edelbrock performer chip, shorty headers, high flow magnaflow cat, and a flowmaster catback muffler.
After installing the new heads and cam I noticed rough idle under load at cruise/low 800- 1500 rpms (it actually ran rough at/around 800-1500 rpms and cruising b4 the heads were replaced), surging at the light and at /around 30-45mph, missing in a couple of cylinders, back fire at the throttle body, black spark plug threads and tip, and hesitation when shifting from 1st to 2nd gear.
In attempt 2 fix the problems I retorqued rocker arms, reset the timing to 0 degrees BTC with the brown connector unplug (my old skool mechanic buddy set the timing at 12 degrees BTC), rechecked recommended plugs (champion r12yc) 2 see if they were all the way in, changed ignition wires( ac delco 7mm silicone), and accel distributor cap and rotor. I also changed the egr valve, it was setting codes B4 the other parts were added. I noticed b4 the heads were installed, when examing the intake the egr air passages were completely block by carbon build up. I clean the passages up good b4 I reinstalling the intake. What really puzzles me is with all these symtoms no codes have been set? What am I missing?