You did all that work to the engine and...

Did you do any work to the fuel system to ensure adequate fuel flow?

You have to remember the sock filter in the tank can become dirty over time and inhibit fuel delivery...you might be getting pressure but not enough volume at higher rpms.... You might also have a crack in one of the rubber lines and be drawing in air?

You are running a lean condition and need to remedy it or you'll be hurting the engine....

I would suggest blowing out the fuel line with commpressed air and dropping the tank and replacing the sock filter....Doc