Dave,

One of the problems may be what your expectations are of the EPA numbers. The EPA estimates are pretty bogus because the tests are run under completely unrealistic driving conditions. So, in the case of the GS450H, the EPA numbers are 25/28. So, let's take 26 mpg as a EPA estimate for overall fuel economy.

If you look at the HiHy, the EPA number is 29 mpg combined. However, if you look at the GreenHybrid's mileage database, the actual is roughly 25.5 mpg. Let's just use 25 mpg to be conservative. That means the actual is about 14% lower than the EPS estimate.

If we apply the same logic loosely to the GS450H numbers, we may expect that the actual FE numbers to be roughly 22 mpg. You do have a powerful V6 engine and the vehicle is over 2 tons. There's only so much FE you can squeeze out of that much displacement moving that kind of mass.

How long are your typical trips? The FE for hybrids are typically pretty bad for the first 5-min or so. Also, what are your typical cruising speeds on the freeways? The wind resistance rises dramatically once you get to speeds in excess of 75 mph. And finally, how much A/C do you typically use? That can also suck down your FE signficantly.