Sounds like you might 'not' have a prop bushing problem after all. The motor will go into the safe mode and limit the rpm's to about 1800, if the motor reservoir gets low. I'd test hop it before taking it to a shop.
Addendum
I just read your other post about the the Yam Precision Blend system.. I'm glad to hear you didn't or won't be removing it. That is a jam up system and pretty simple. Since you have already removed and clean the sending unit and it ran good, that's probly all it will need. If the system is clean it will work flawlessly. The main tank pump rarely fails, from what I read, but don't ever take it apart without marking the little gear looking do hickeys, replacing them the same as removed.. I could tell you a horror story on that, but won't embarrass myself with it. Being electric, make sure the wires are in good shape, and if it were me, I'd replace the check valve in that oil line near the main tank, just so I'd know it was new. Fuel pumps are pretty cheap and easy to replace, too, as well as thermostats. Could be all these things were replace in that 2.6k tuneup, but I doubt it, if it included a new powerhead.
Like TC said, check the carb lines to make sure there isn't anything restricting the oil flow, but if it ran good before the oil problem you described,they are likely ok.
You sound like a 'do it yourself' person, and if so, get a factory manual, and read it. You can head off a lot of problems by doing routine preventative maintenance . You can get a manual here. http://www.iboats.com/Marine_Boat_Motor ... _id.216500 The cost is about 60 bucks or so, but will pay for itself many times over.
Also, Iboats has a very good Yamaha forum, as well as other motor makes, for further research, or if you want to just learn what to watch out for.
Like I said to your other thread, good luck, and if you are a new captain, be careful and equip your boat for that emergency we all hope will never happen. Q
Newbe update.
Moderators: bman, Chalk, Tom Keels