IT probably is just the price you have to pay at the pump is more than you are used to.My local gas station went from $2.99 @gallon to $3.08 @gallon OVERNIGHT!!!!
Needing a tuneup
Does it have a plugged O-two censor?
Prices are going up all the time,maybe that is the answer.
As the price of gas goes up it becomes a more valuable commodity to steal. Maybe someone is siphoning gas from your tank at night...buy a locking gas cap and see what happens to your fuel consumption.
I'm not a mechanic like insomniacSeven, yet my guess is to have a different mechanic do an overall check of your car. Maybe something wasn't hooked back up properly when they changed the alternator. I had a mechanic put a new tire on the wrong way when they checked my brakes. When I took my car in again, another mechanic caught the mistake. My tires are all black and it wasn't that noticeable. Maybe my original mechanic was in a rush or distracted and made the mistake. That is possible for you too.
maybe you have a leak in your gas tank
If I had to guess, it's the O2 sensor. Is there a "check engine" light?
Chances are it needs the air filter replaced.
Release the hand break! You would be surprised at how many people will drive with it on and not no it.
Have you been driving under the same conditions as normal? In the same area?
If it is an automatic transmission,check your fluid level. Could the tranny be slipping?
Does the car feel as if it has as much zip as normal? Does it feel some what sluggish?
Time for a tune up!
change the air filter, fuel filter, change the oil, get a tune up, make sure the tires have the right pressure and use a fuel additive.
and drive more cautiously, if possible.