Your RX300 is doing the best it can with what it has. Some reasons why: The 2002 RX300 has a coefficient of drag of 0.36. The 2013 GX460 has a coefficient of d

Your RX300 is doing the best it can with what it has. Some reasons why: The 2002 RX300 has a coefficient of drag of 0.36. The 2013 GX460 has a coefficient of drag of 0.35. The GX460 looks boxier, but it's experiencing similar air resistance. The RX300 has a 4 speed transmission. The GX460 has a 6 speed. This gives the GX460 (at least) two overdrive gears while leaving other gears optimized for performance. The RX300 makes 200 HP at 5800 RPM and 222 lb-ft at 4400 RPM. The GX460 makes 301 HP at 5500 RPM and 329 lb-ft at 3500 RPM. More torque, at a lower RPM, lets the overdrive gears be more aggressive, letting the engine run at lower RPM and use less fuel. The GX460 does weigh more, but this is likely outweighed by the other factors. Also, weight is less of an issue at highway speeds on relatively level ground. The GX460's 1UR-FE V-8 is not direct injection. The 1UR-FSE it was derived from has direct injection. The other comments are also valid: newer engine technology may make the 460 engine more efficient in other ways.