Also check your valve spring pressure. Could be floating the valves on top end. More noticable in high gear. Car just lays down. We got a bad set that crapped out on 3rd pass. From around 6000 thru 6400 the car was just flat.Company rep. told me they had a bad run of springs made good on the springs. Woke it right up and we turn 6900 now with no problems. Just a thought. Good luck!!!
