[bartimus]

Is it possible that the mechanic made a mistake while installing the timing belt? If your valves are not opening at the right time, that could affect the mpg. On my previous car ( 2000 Forester), the mechanic used the wrong belt (which had alignment markings slightly different) and I started getting misfires. It was a small mistake so I didn't seize the engine, but a big enough mistake to cause tons of issues.