I had a problem a few months ago when i set the valves at zero after putting in a new head gasket. Ran great the first practice session. Next time out, it was down on power. Checked the valve lash again on the engine with the new head gasket the next day and realized the valves were not completely closing. Guess the head gasket compressed enough to affect the valve lash. Reset valve lash and is still perfect after multiple practices as well as running the CKNA grand nationals up front.
Lesson learned: reset valve lash on engine with new head gasket after a heat cycle or two. First and only time this ever happened. Was setting the initial valve lash slightly higher in the past after head gasket replacement.