Most of that high end motor falloff is usually a mixture TOO rich- try more oli in the gas.
here is the way to tell first- adjust the petcock closed down a little- if this ends or helps the fall-off, it's because the mix is too rich otherwise, not that it's not getting enough gas, which everyone usually first assumes. It's actually getting too much and drowning.
the other thing is your first statement about the motor being "torque oriented) or something like that you said. YES- this is sorta true- with a stock carb, I don't think many people have much luck in that high whiny range at the top-
when I switched from the stock 44 to the 36, it helped a lot, mostly though at cruising WITHOUT the throttle wide open- in the range that some people call "4 stroking" here (and I'm not sure about the accuracy of that term). So my advice is aim for a good cruise speed- and don't worry about top end- the motor will run longer and you won't be so likely to hurt yourself. Don't be afraid to put oil in the gas- the motor needs it.
I have both a 34 tooth sproket that is a bike front chainwheel I'm drilling out, and I als have a 32 sprocket I got from boygofast on e-bay (search bike motor on e-bay and then go to boygofast store when his items come up) It's about $20 and shipping- I think he takes offers. Haven't installed either yet, so I can't attest to the effect. The 36 certainly gained some cruise speed over the 44, but at that time I was living in some severe hills, and probably wouldn't go any lower there. Now I'm in flat lands, and may.
the 34 I got for $11 delivered from bikeparts4 you also on e-bay- I'll post it next. You'd have to drill the center and i've already drilled it to bolt directly onto a large falnge alloy Schwinn 10 speed hub.