Have noticed when driving in high heat environments (Phoenix, Sacramento, Palm Springs) that the mileage on the FEH decreases dramatically.

The driving style is, at the speed limit with air conditioning on. The mileage decreases usually about 3 mpg using the same driving style as in cooler environments (going to San Diego).

Just got back from Phoenix (115 degress) and the FEH seemed very sluggish in the heat.