Proper Prop

I have finally broken in my 2015 Triton 17 PRO with a 115 HP Suzuki. The prop is a Solas 9431-130-19. Max I can get is 40 mph with this cool water but it seems like I have more power left when I hit the 6000 rpm max. Any ideas? I don't have a jackplate. Would that make a difference? I have read where others are getting 50 mph with this setup. I am not even close to that. Speed isn't a major issue but I want the boat to perform at it's best. Hole shot is good. Anyone with a similar rig have ideas? Thanks for the help.