I had my 30,000 mile service at Sierra just before Christmas -- replace PCV valve, lub, oil, diffs, trans, TOD, etc. -- and since I got the car back the MPG has gone from an average of 16 to 13.

The car is not running rough, no smoke or strange noises, idle okay. Any idea what could have been resete, disturbed, left undone or ? that would cause this drop in milage?

Thanks.