I have a 1991 GMC S-15 jimmy 4x4, has the 4.3 idles rough and likes to buck in gear.?

I have replaced all tune up, plugs, wires, cap, rotor, fuel filter, changed the EGR valve, the ignition control module, temp sensor, and even took off the catalytic converter. I took off each plug wire one at a time, no change. You can hear it popping through he exhaust, I have not taken off the muffler maybe that is clogged?? The injectors seem to be loud at times, like they are working really hard. When you are driving it seems to run ok, no misfires when driving. Its weird and its driving me nuts, any help would be very much appreciated thank you!