Originally Posted by Andrey

I guess I'm also on the side of those who get at most 300 miles on one full tank. Granted, I have S/C installed, but even without it I never got 400+ on the tank (22.2mpg) even when 4Runner was brand new and driving straight on interstate. So I'm pretty sceptical about 23 mpg claims that some are making...

One possibility is that your engine is an exception, but as we can see from this thread the mean is around 18-19 mpg. So, it would be very practical to say that unless you've been getting 22+ mpg to begin with, there is no magic that will suddenly make 4Runner run 400+ on a tank, especially towing 1k load.