Plug reading

They heat range is fine and I run that plug on our
street/strip cars. BUT I do not idle it for extended period of
time any more other than at traffic light and such.
Ground straps look about right.
Examine the porcelain for specks on them or post some closer
pics of them ( My eyes are elderly). Lacking that you are fine.
But 84 jets?
I would be 74 to 76 at Sea level and one smaller size for every 1000 ft
of elevation you are at.