I ran for quite a while with the stock belt when I switched to a 3.4" pulley. My stock gauge never went over 9.5 lbs. When I switched to one size smaller belt, I didn't notice any difference except the tensioner wasn't right at the end of its travel like with the stock belt. Only under certain weather conditions, cold and wet, will it read 10 psi.
I don't trust the stock gauge. It'* quite possible that it'* off by 1 psi.
Don't worry about it.
I always run 94 octane.
I expect now with the opened up exhaust to make about 2 psi less than before but it will make more power and allow me to probably go to a 3.25" pulley to get back up to 10 psi.