Gas milage issues

My 04 Grand Am sucks gas like water. It takes me 1/2 a tank to drive 1 hour on the highway traveling 65mph! I have checked the fuel pressure and it's normal. I have tried several bottles of fuel injector cleaner. I changed the air filter even though it was relatively clean. My tire tread is at 3/32 all around (I'm getting new ones on Thursday). I don't know what else to do! Please help me someone!

How many miles does your GA have on it? If never done, it may be time to repalce spark plugs, spark plug wires, front O2 sensor' Do you have a 4 or 6 cyl?

If you have a temperature gauge, is it reading normal temperature? as in not too low?

Have you checked your tire pressure?

What about the parking brake?

Do you have the check engine light on?

Do you smells gas?

What about your acceleration habit?

Is your transmission slipping?

At least go to one of the autoparts stores that will check the car's computer codes for you for free, and if there are any, write the numbers down. If you're not the original owner, be aware that sometimes the check-engine or service-engine-soon lights are broken/de-activated, and there may be codes with no warning light on.

If you know someone with a better code reader/scanner, have them scan for "history" or "pending" codes as well. The codes will point you in the direction of the problem; also, knowing that there are no codes will help to point to things which may be the cause.
You should be getting at least 25 highway/20 city, even with the V6.
Hope this helps.

I have 136,900. I realize that I probably need a tune up. It shouldn't cause my gas needle to move down two notches just driving 10 minutes! I have a V6. This problem started about a month or two ago.

My temperature guage reads the same as it did 9 months ago (1-2 lines below 200).

My tire pressure is normal (set by a dealership).

I have never touched the parking brake.

No check engine or warning lights.

Severe gas smell inside the car when I warm it up before work in the mornings and sometimes when starting.

I don't stomp on the gas pedal.

My transmission isn't slipping now that I tightned the loose transmission pan!

Computers at Auto Zone are designed to only read when the check engine light is on. Mine isn't and never has been in the 9 months I have owned it.

strong gas smell seems to indicate a fuel leak.

Investigate it. You shouln't be able to smell gas, the only smell you should be able to smell is the exaust... Surelly not gas.

If you have a leak, not only you waste money and contribute to global warming (yeah who care anyway), but you also put your car and life at risk, as a leak mean fire hazard, which mean you could be trapped in a car in fire, where you can't stop right away (think on the highway).

Now, it could also be unburn gas, which if that is the case the computer should have a code for it.

Sometimes the check engine and/or service engine soon light bulbs burn out. When you start the car, they should come on briefly, then go out to let you know that they are still good.

Is the car still performing/accelerating/idling OK? If so, you probably do have a fuel leak in a gas line somewhere, and it could be very dangerous. Have you seen any gas dripping under the car? Let it run in your driveway for a few minutes, see if there's any gas dripping.

And, sounds like you've had a transmission fluid leak in the past, did you have the fluid replaced, or topped off? Has the fluid level been checked?

Hope this helps.