after 60 mph boat starts to porpoise,need to trim almost all the way down,496 mag bravo one with miriage 21 prop,max speed is 64-65mph

A Bravo 1 4 blade should get rid of the porpoise. The 21" seems a little small as well. I would think you should be able to spin a 23"

Try a 22" Bravo 1. A Bravo 1 prop eliminated nearly all the porpoise on my 24 Outlaw that I used to have.

Cruise speed will go up, but top end will lose a couple mph.