Help with 2014 Yamaha 25 Hp 4 Stroke

Recently been having issues with my 25hp not running correctly. The best explanation is when it gets to about half throttle there is no more acceleration, but the rpms seem to still increase. At least it sounds like it. Replaced the prop, still the same issue. All the parts, too include thrust washer, spacer, and nut look to be in solid condition. No hub to spin, but it feels that way.

Outside of something inside the lower unit, anyone.have a simple fiz or heard of such symptoms? Really not looking forward to taking it to the shop!