When i first recieved my car about a month ago i got about 260 miles to the tank. Recently my car has been acting weird and i got a tuneup (new plugs, plug wires, air filter, fuel filter, cap,) A few days before i got this tuneup i noticed my fuel gauge dropped by half a tank in a matter of 30 miles! Even 2 days after my tuneup i am still getting the same bad mileage...Any suggestions? Bad gas or broken gauge maybe? Any input would be appreciated