I ran into that years ago. I worked at a garage and a local guy had a Ramcharger that he put a 440 in. He had the machine shop build the engine and he put it in. It done the exact same thing. Sounded good at idle and would rev like crazy. He changed everything atleast 2 times and finally give up. I pulled the timing cover and the timing chain was off 2 teeth. I lined it up and it would pull to 6000rpm no problem. Before it would go to 3000 and stop. Even holding it to the floor it would set at 3000 all day long.