It sounds like you just need a simple rebuild for get that power back.
i would suggest a complete motor tear down, inspection and rebuild, due to its age.
Chances are that crank has some wear and tear and it would suck to rebuild the top end and have the bottom end go boom.
Any of the site sponsors can rebuild the entire motor for you if you're not mechanically inclined.
There's likely one close to you that you could even drop it off at.