Here is your answer. Your new tune up has increased the engine performance of your Sienna back to near original state. Siennas are designed to run on 87 through 93 octane...but they prefer high octane of 91 or 92 octane, and they run better on it, and it gives better mileage as well on high octane. Lower octane causes knocking in the engine, low power, and worse gas mileage. Try a fresh tank of high test 91 octane Shell or Chevron, Exxon, or Texaco. these are the gases most preferred by Toyota and are called high tier gasoline (far better gas for your engine) Good luck, here are two links for the appropriate gasses you will do best with in your Sienna.
http://www.toptiergas.com/index.html
http://www.toptiergas.com/retailers.html
2001 Toyota Sienna - It sometimes sputters when going up hill. What's wrong with it?
Linear Mode
