I have a 2002 Ranger 520VX with a merc 225 optimax. It has a 25p tempest prop. I can only get around 63 mph on topend and it will only turn around 5100-5300 rpms. I don't have a clue what to do. Any advice would be helpful.

the 225 opti should be running at 5800 rpms.  sounds like a prop problem to me.  i have a 21ft stratos of the heavy kind from '99 and a 225 opti on it.  i ran a tempest on mine that pushed it around 72mph at 5800 rpms.

one caveat, my tempest was pushing me around 64 - 65mph and then i sent it off to a guy in alabama, i can find his address for you if youd like.  he's a magician.  i described the problems i was having, sent it off w/ $150 and got it back 6-7mph faster.

You should be able to turn a 26p prop 5600 to 5800 RPM ....  maybe a prop problem ...... also .... how is your boat loaded it's easy to load too heavy in the front end. You need someone to work your prop to add some lift. Marks Hi Performance Prop will work your prop to the specifecs of your engine and hull combination ..... send me a PM and i'll give you the contact info for Mark. BTW, he turns propsout of his shop in 24 hours !!!!