1988 GMC Sierra Engine miss

I changed plugs, wires, cap, and rotor. Engine still misses. At idle you can hear it missing, and it makes a popping sound in the exhaust. By pulling plug wires one at a time, each one seems to slow the engine down and it idles rougher. Engine misses while idling or going down the road. It also misses under acceleration whether mild or wild.

Any Ideas?