Just took my boat out and tried the used 15 I bought. The motor runs great starts easy and shifts good. My problem is I think the prop is slipping. You can be going along at 3/4 throttle and it just all the sudden revs like its out of the water. When you let off the gas it catches back and pulls again. I tried running it at lower rpms and it only does it at 3/4 to full throttle. My question is where an what kind of prop do I need to get? I fish only in the river near my house and my boat is kinda heavy. Thanks,Brian.