Rolling road then miss fire

[Oggers]

Well pulled a plug today and looks ok? Are they the right heat range for a s/c truck?

 

[Michael from the U.K.]

i had the exact same thing on mine, turned out the locking pin for the harmonic balancer had sheared allowing the pulley to slip on the crank.Realigned the balancer and fitted Roe heavy duty dowels and its all good.

 

[Oggers]

Had another run out in the truck today. Sat in traffic for a wile water temp just above 200. Filled up with fule then it started to miss fire, again in bertween about 1200 to 2000 rpm. Above of below this it's normal. When it was spluttering the a/f gauge was a little erratic.
It seems to only miss fire after it's been hot and then switched off and re started.
Thoughts?
I'm running Gibson headers and have read there not the best for keeping things cool.