I have a 2003 Mazda Tribute with the Ford 3.0 V6. I just replaced one of the ignition coils, no miss, but now it has come back. No CEL light though. Bad plug maybe?

I have a Mazda Tribute with the Ford 3.0 V6. It had a CEL light on which
was related to the EGR system, that turned out to be a broken wire to the
vacuum control solenoid for the EGR valve vacuum line. But a few days
ago the vehicle developed an intermittent miss. The next day the miss
became constant and caused the CEL to flash. Took it to AutoZone and
had them check, turned out to be a bad ignition coil on the #6 cylinder.
Fixed that at the same time I fixed the broken connector wire to the egr
vacuum control solenoid. All was fantastic, got the car inspected this
morning and it passed with flying colors. This afternoon on the way to work,
the miss returned, but no CEL on. Vehicle has 199k miles and I have not
had the plugs changed nor the ignition coils except the #6. I bought it late
Dec 2015 and have put about 15k on it. Not sure what maintenance was
done to it before I bought it but it does appear to have been maintained
regularly. Could it be plug(s)? Would a check with the code analyzer show
anything even without the CEL on?