[spaldam]

I've got the 6MT with TRD package (i.e. BFG's). I get around 15-16 on average, mostly freeway at around 70 MPH. I also can't go much slower then 45 in 6th without lugging the engine and that's on a slight decline. 5th does fine above 40ish.

Keep in mind that your driving habits will have a big effect too, and just because your going slow in a high gear doesn't mean you're getting really good gas mileage. If you travel faster, using the same amount of gas in the same amount of time, your MPG improves because the distance you traveled in that amount of time also improved. If you have to push on the peddle too much, you'll do better if you down shifted.