Can the Toyota dealer buy back the car?

Keep in mind cars are very complex and some random issues are hard to diagnose and can require trial and error to find let alone fix, especially what youre describing. They will have to find somewhere to drive it at those speeds and the problem will have to present itself while they are driving it. If it doesnt act up while they are driving it, they cannot diagnose a problem in some cases. They also have a ton of other customers cars to fix as well so they cant drive it all day. Im not defending them or taking sides, just putting it into perspective as I used to have to try and explaiin that to people when I was mechanic. There are buy-back laws too that vary by state. See "lemon laws" in the owners manual or talk to your secretary of state to see what constitutes a lemon where you are. Generally it involves having to fix the same problem over 5+ times without a lasting solution. Being that its a 2009 it may be too late to do that but check into it to be sure. If you are elligible for buy back you can use that to your advantage. contact Toyota itself and if you are approaching buy back criteria they may decide to put a whole new engine in the car for you under warranty (or whatever they feel will erradicate the issue).

Hopefuly the dealer has put you in a rental since its taking so long. If not, ask them to. if they have to pay for a rental for you or use a car on their lot, they will try much harder to get it fixed faster. I deal with similar issues now as I work for Audi/VW corporate now and beleive me, dealers get motivated if you're costing THEM money.