Howdy folks. I'm wondering if anyone has ever had a problem like this. I bought a used 23 hp vanguard mini with high performance cams and a bps exhaust. I have had problems with the motor losing power on the top end. I happens more so with the load. Other guys have the same motor without the upgrades and don't have near the problems I do . Thought it might be a fuel issue but buddy told me to put a fuel pump on and it should help it. The engine seems to overheat and lose power. Tends to backfire. New short block. Help please

It is on a 16' 48" alumacraft. Once on a plain at full throttle it's like looses compression and power. Has a rev limiter and threw a rod. Hence new short block. Go back to stock? Too much of a load?