Congratulations on your new purchase! I also bought my boat in Bellingham (From Bill at Bellhaven Yacht sales) and I also am wondering about my prop....
You could definitely have fouling on the hull or the prop. A neighbor of mine, with a newport, had barnacles on this prop and could only do 2.7kts. He cleaned off the prop, but not the hull and was up past 6kts.
Michigan wheel has a long detailed online form that will tell you what size/pitch prop you should have. You could fill that out and see what they say. You should also look at your engine manual and see what rated your rated RPM is and if you are getting to 80% of that or not.
If you're not getting to rated RPM you could have a throttle linkage problem, fuel starvation problem, mis-sized prop, underwater fouling, old/bad fuel..... etc.
Enjoy your new boat!