Take off the s/c belt and see if it still happens to check if it's false. Or you can dump a gallons of 104 race gas in it to see if it goes away. If it does, it's probably your tune. I had 4-5 degrees of KR with headers, 3.4 and other supporting mods sitting at 9.5:1 a/f . leaned it to 11.0 and got zero kr.