RPM to high & low mph

Hi I have a nitro 750 2007 w 90 hp, my current prop it's a Michigan vortex 12.75 x 21p alumnium
and I run the boat in WOT. @ 6400rpm an reach 39 to 40mph
i think its to high rpm and to slow for top speed....
I make the exercise in the web site of mercury marine (prop selector) and says I need to change the prop
for a lazer 2 13.3/4 x 23P or trophy plus 13.3/4 x 23P or 24P
do you think its real?
or what I need to do to get overall well performance?

You might want to check and see if the prop hub is bad.

its brand new prop hub...that's why it look's to me wired
tnx for you reply

Call Steve at Steve's Custom Props. Great guy and he can answer all your questions.

OK I will... Tnx. for your help...
any one has this issue?

Higher pitch prop. Go with the 23. See if you can test one out

I do not think you need to change a lot. I would try a 13 3/4in. 21 pitch first. The diameter is pretty small on your 21.

ok ..I try for a biger prop and the same pitch
and then will see if it's better a high pitch
tankyou for your help