Started skipping around at idle.
Checked and had 30,000 miles on my plugs.
Put in a set of NGK FR4 (5155).
After over 60 years of using primarily Champions thought I'd try NGK.

 

Copper core is usually good for around 30k anyway.

 

Tried to post photos but didn't work.
That's longest I've ever ran a set of plugs.

 

I just changed my Champions. 50,000 on them

 

On mine the gap had grown from .035 to over .040.

 

Just an update.
I had a occasionally rough idle and then it started idling around 1500 RPM or a little more and check engine light came on.
Code reader said multi misfires & No. 6 misfire, high idle.
Plugs took care of the misfire but not the idle speed.
Replaced the lifetime AIC Auto-Zone valve with an Borg-Warner one. All is well so far.
Didn't check for blown plenum gasket but uses about 1/4 of an inch of oil on the dipstick in 8000+ miles.