After cleaning the truck today I noticed a very nasty smell at the rear, looked at the tail pipe and the inside is covered with pure black soot. This engine was smoking a little bit on cold start only, puff and its gone. I started it a few times and sure enough puff puff, let it run a few minutes and it cleared up, few minutes latter puffing blue. I hope valve guide seals will do the trick this time. I was having no problems with engine other than a puff at startup using M1. This super tech syn oil (wall mart special) has only been in the truck a few weeks. I also checked the oil, its not low yet but has the same nasy smell thats coating the tail pipes. Guess its not M1 packaged different after all.