Want Eliminator 454 Jet boat to go faster

I recently bought a mint condition 1987 Eliminator 20.5 ft jet boat. It has a 454 indmar engine with msd ignition. I believe it is the ho model. It has the Dominanator mb12s jet pump. I'm only seeing 50mph, and thought I should be seeing much more. If you put it to the floor from a idle within 1/2 second it's at 5000 rpm and stays there. Loaded with 8 people I get 46-4750 rpm. I want to see 60mph with me and a few people, which its at 50mph with a few people. So looking to gain 10mph. Any help would be appreciated

Want Eliminator 454 Jet boat to go faster