Same here (ditto what Mr Kite said), per the official Toyota service bulletin to go with the 5W20

I think I am done with the 40 mpg tanks until next summer. The cooler weather is already taking its toll on the warm-up hit when I leave work. My most recent tank didn't hit 40 mpg. It was 39.6 mpg after 545 miles according to the display and 38.6 mpg after 564 miles according to my calculations. This particular tank had to overcome some interstate driving at the beginning of the tank.