More top speed for my Spartan!

[SouthpawSpartan]

First off, I really enjoy this site! Tons of helpful people and awesome boats!!!

Bought a Spartan 2 months ago. Upgraded to Kintec 5" Dual Pickup Rudder and Kintec aluminum Water Jacket. Everything else is stock. Rides really smooth now, but I've only managed 37.3mph via my gps on 6s. Is this normal? Really want to get this thing 50+

HELP!!!

Thanks!