Having changed my RX 400 for an RX 450h I have had the same experience i.e. compartively good mpg figures(32/33mpg) on the 400 and relatively poor on the 450 which is averaging 33 mpg some 12mpg short of the claimed target. Interestingly, my best tank average has been 36.5 on a recent journey of 250 miles, mainly involving motorway/dual carraigeway driving. I was travelling north to south, maybe it was downhill!!