I have a lower end of a 04 right here that the customer was having the very same issues as you are describing, and we could only get it to act up for us by strapping it to the dyno and waiting until the motor was really heated. Everything checked out fine... head, and valves, and clearances...etc. We decided to rebuild it and his crank bearings and crank were showing some scoring and IMO was about to seize... and he was experiencing mild seizing.
I ope this is not from the 07 in your sig?
I ope this is not from the 07 in your sig?