Bat sounds like we ride in similar conditions, I am at 5000-->8000', before I rebuilt my engine I was running 140/142 mains setup like yours, and was having a stalling problem, went to the 25 pilot and it all cleared up with no other changes. after the rebuild with the high comp piston and all I am at 146/148 I still am using the 25 pilot but I am noticing a white spot on my plug. I still have a few hours to properly break in but I might have to go to 27.5 pilots

 

I would also check your exhaust. Make sure your pipe is on tight, and that there are no exhaust leaks.