GT125 stalls at high speeds

Hello riders,

My GT125 stalls when I’m driving full throttle in 5th gear, around 95+km/h. When engine braking it has problems with getting up to power when opening the throttle again.
I’ve already checked for air leakage. but non found. I’ve cleaned the fuel pump changed the fuel filter and checked the tank valve. All looked fine. At this point I have no idea where to look.
Any suggestions are more then welcome.

Nathan