Did you ever get 43mph out of it before? Or has it always been stuck at 35mph?
Just asking cos 35mph sounds good for just the cdi cut, without the smooth boss. Howdo you know for sure the boss was changed? Have you actually taken off the variator and looked, or are you taking the previous owners word for it? If your not 100% sure then i would take it apart and double check it is smooth.
My derestricted agility did 34-35mph after cdi cut, around 43 mph after i fitted a smooth boss, and now does 48mph easy since i fitted a race variator.
I ran it for a few days on the #80 stock jet till my #82 jet arrived,and i still got 43mph, the engine sounded a lot better wit the #82 jet, but i still got 43mph with the #80 jet in.
Kymco's official recomendations for derestrictig an agility is , smooth boss, cdi cut and #82 main jet, i saw the printout at my Kymco dealers. Tho i have heard at least one other person on an agility having to use a #84 jet to get it right at plug chops.
Double check your boss tho 1st if your not sure it has definately been done.