So Lexus used a different tune to get 9 less HP and 2 more torques from the same engine, and it made it require Premium Fuel. Nice.
2010 Tundra 4WD Double Cab (4.6 V8)
Fuel type
Regular unleaded
EPA city/highway MPG
14/19 MPG
EPA combined MPG
16 MPG
Horsepower
310 hp @ 5,600 rpm...
What bugs me about this is the Tundra used the same engine rated for more power/torque, and does not require premium fuel. Economy is marginally lower on the Tundra but I'd expect that's more to do with aero/weight/tire differences.
As one data point the Tundra was available with the same engine with a marginally different rated power output, and does not recommend/require premium.