I believe our Ford TaurusX has the same Drive train as the Flex. The manual advises not to tow faster than 65 mph but I have caught myself exceeding 75 mph a number of times with no problems. However, I do try to drive and tow a little slower than 65, primarily for fuel economy.
Sold the Motorhome, joined the fully retired gang. '07 Winnebago Journey 34H, ISB-02, MH2500
Toad - '08 Ford Taurus X, Blue Ox, Aventa
US Gear UBS