[Lemans64]

Have seen issues as u describe, runs great when cool or short trips, extended trip it will start to sound like noisey lifter then develope into an engine miss, and after some cool down or some idle time problem will dissappear. Carboned up exhuast valves, carbon builds up on the valve stem and gets past the carbon relief on the valve which causes the valve to stick in the valve guide when hot, causing lifter noise and engine miss, after cool down problem goes away. There are some injector flush chemicals u can spray down the intake to try and loosen up, but permanent fix is to remove heads and clean valves and guides or have valve grind done. Just my opinion though, u should have a professional drive it and give their opinon.

Rick