Hello Howard,
Welcome to this site. You might look in the Prius forum and post your question there, since your Highlander Hybrid's Hybrid Synergy Drive is similar to the Prius'.
Do you take your THH on long trips? Has your high voltage battery pack's state of charge dropped? I'm thinking perhaps your HVB is low, forcing your engine to run more. Some retired friends of mine took their THH from CA to UT, and got their best mpgs ever - 30 mpg.
Toyota put out TSB EG018-06 which allows '06 Highlanders with the 2AZ-FE engine to use ILSAC GF-4 0W-20W oil. That thinner oil might boost your mpgs 0.4 mpg.
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Darrell
Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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