im begginning to wonder if you have something loose floatin around in the intake manifold, bouncing around and sticking under a valve, holdin the valve open piston hittin and bustin rockers? sounds like it would destroy a valve or piston first but maybe not... guess its a possiblility....stranger things have happened...about the only other possiblilty is the cam timing off a tooth or two... it could still run great untill certain rpm...
