atdg - I would first look at all the stuff that affects performance including the cleanliness of the bottom of your boat, how long since a tune up, unnecesary weight on board...
You might also want to take the props somewhere to get them checked for the proper pitch. I got hung up on my old boat because I assumed that the props were the pitch that was stamped on the side. The guy before me had taken them to a shop to have the pitch changed. I was going back and forth between two props that were identical and I couldn't unterstand why the boats characteristics didn't change when I swapped them.
Jim