i have a 2000 mc ls. recently developed an intermittent starting & stalling problem. sometimes is fine, other times starts for a couple seconds but runs rough then dies. usually starts up fine in under 10 starting attempts. going down road sometimes just dies. a cam sensor code came up so i changed it out. same problem. meanwhile blew a head gasket. repaired that but had issue with rockers coming loose. while checking rockers, intake off, i was turning engine over by hand. when only 1 thru 6 rockers tightened with push rods in, a loud clanking noise came from cam area. sounded like something broken loose & rattling around. with all 12 push rods in noise was gone. ive never gotten into cam or timing areas on this motor. any ideas on noise or start stall problem??? thanx