Les, I was very impressed when I read the Car & Driver review of the 2006 RX400h. Not only was it faster (0-60 in 6.6 seconds) than a Porshe Cayenne but it got superior gas mileage and would inevitably be far more reliable. Not too long after we bought ours, gas prices surged to record highs.
I think that Lexus, like all other premium brand manufacturers, favored power and speed over all-out efficiency. The first Honda Accord hybrid followed suit. The Camry and lower cost Lexus hybrids veered toward higher efficiency. The GS450h was not one of these. It could do 0-60 MPH in 5.4 seconds and average 30 MPG, starting with the 2013 model. Now we have the LC500h that hits 60 MPH in about 4.7 seconds, not as fast as a BMW i8 but far less expensive and more reliable.
By the way, I once owned a 1968 Cougar with the same engine as your Maverick. That Cougar probably got the same mileage.😃