missing when stopped in gear. on 1991 Chevrolet 1500 Pickup

missing happens when stopped but does not die, but runs just fine otherwise. I have replaced the EGR valve, o2 sensor, fuel pump/filter, oil sending unit. What else can I try?

2 answers
STOP TRYING PARTS before you go broke and your truck is still not fixed. Have your vehicle diagnosed!
you might have a bad iac valve or a bad egr silinoide