Anyone have this happen? What is your diagnosis??? Appreciate your thoughts.

Im thinking head gasket. Get a compression test done. The extreme compression of the cylinder(s) is forcing the fuel mixture into the coolant system on the power stroke. It may not be a big enough leak right now for coolant to drain back into the cylinders whens its not running, but it can quickly go that direction. Hope its not, but thats my thoughts. If this is the case, you may notice excessive heating, coolant overflow, and air trapped in the coolant overflow tank.

Does sound like a head gasket. That's about the only time the fuel and coolant are close enough to mix.

Jake

Funny though I'm losing coolant (no noticeable leak) and the truck is running spectacular. I figured anything other than fuel in cylinders and it would run terrible. Just a note that the engine has 5000 Km on it. Was just about to celebrate the finish of the break in period.

Yay not....