I have a 2006 38 EC with the same motors. First, make sure you have the mercuiser XR props. Four blades on leading prop and three blades on trailing props. Next, change out the plugs and more importantly the fuel filter in the fuel cooler mounted on the engines. Those filters should be changed every 100 hours. I let mine go and the boat slowed down significantly. I was able to get to 62 mph on my gps speedo at sea level in fresh water. Before I changed the plugs and fuel filters, I was don to about 56 or so. Interesting though, I did try some bravo 1's 1.5:1 ratio with 26" four blades and managed 65 mph and that was overtrimming to get the rpm's up. With the right props, I bet I could have gotten a few more mph. That's my $0.02. Good luck to him!!!