In the true spirit of troubleshooting... never assuming anything...
You mentioned new components have been installed so my situation may not be relevant for you.

I had a dying-at-high-speed problem one year that I traced to a leaky fuel line junction where the hose joins the engine. I found that the engine would keep running fine if I kept squeezing the primer bulb in the hose. Fuel also squirted out at the junction another sign of a bad seal. So air must have been drawn in when the fuel pump was working hard. I learned the hard way that the Tempco (spelling?) replacement end piece, supposedly compatible with my engine... was not. A new Honda hose assembly at huge expense solved that problem.

Another time, the high speed jet had clogged. In that case, the engine never developed full power until I disassembled the carb and cleaned the jet. I admit to not treating the engine very well over the winter, so three years ago I had to buy another carb and gaskets for $162. Seemed a better value than $47 for a fuel hose and spark plug another year.

Let us know what you find out!