Recently I went to babusar top for chai I was on ybr and my mate was on gr150. It was 22 hrs ride and rest and we reached back in the same day.
GR150 failed to perform at high altitudes. Extreme missing and only working power band was at 1500-2500 rpm in 1st gear. This was so surprising for us.
So we were also looking for others if they face the same issue and I ended up on your thread.
Initially what we diagnosed is that the mechanical carburetor was the culprit here (gs 150 never disappointed with CV carb) and we were looking for options with which one to swap.
"Replaced the stock VM20 carb with a cheap VM22 carb from aliexpress" outcome of this? @gull_s_777