God, I hope you don't have a messed up 502 like I had in my boat when I bought It brand new, the shop tried damn near everything to figure out what was causing the lack of performance. After about three months Merc ponied up for a brand new motor and I picked up an instant 9mph. If you want shot me an email and I'll send you my number and we can talk about the many things that were tried. The shop never received any feedback from Merc about what the problem. Good Luck, if I didn't know what the boat should have done I never would have guessed there was a problem the engine always ran great just didn't have the power, sh_t I couldn't even get on a plane with 5 people and a full tank of gas unless I put the tabs down. I was getting about 61 on the speedo (57.4 gps). Let me know if you want to chat.
Larry