on their(KB) site they want .004 piston to wall clearance on the top ring for each inch of bore with forged(not hypereutectic) pistons(If I am reading their site correctly,it was a little confusing) which would put you at .016" for a street normally aspirated application(the top ring). At .012 you are tighter than they recommend but I dont know if your rings are butting & causing the problem or not but the more I think about it I would be inclined to think the rear mounted battery & long cables are the culprit. When its warmed up it cranks too slow & this is the issue right? At that point in time could you pull the plugs & see how it cranks & also with the plugs out put a socket & breaker bar(or torque wrench) on the front harmonic dampener bolt & see how hard it is to turn ? or easier yet at that point in time get a jump directly to your starter & dont use your trunk battery & see what it does. It is midnight here & I am going to have to sign off. I will get back to you tomorrow. Post what you find out.