Car seemed to be missing and I ran a cylinder test where #4 came up as a problem. I pulled the plug and its all gummy. No other codes turned up on my code reader. See photo below of gummy #4 and a clean #3. This plug was pulled after about 4500 miles of city driving, and after upgrades including GT-40 heads, Comp Cam studs, rocker arms and pushrods, Cobra Intake and 65mm TB. What concerns would you take away from this? Thanks for any advice.