Firebird Overheating need help

I have a head scratcher for you, i have a 95 firebird 3.4 and it is confusing me, i bought it used with 160000 miles on it, and it has an overheating problem. I have tried everything, the car starts fine on the first turn of the key, i have replaced the thermostat 3 times in the same month, i have also changed the heatercore, the cooling hoses (all of them) the radiator, the waterpump and the fan. NOTHING IS WORKING. the car also gets horrible gas mileage like 10 in town and 17 on the highway if im lucky. If you drive the car it gets hot like in the 235 range, on the highway it stays at that temp, and if you drive it over 70 it climbs into the red zone. I have checked the water lvl and there is no decrease, i have checked the oil and it looks fine which leads me to believe the headgasket is fine too. i have had many mechanics look at it and they are stumped. I have not done a compression check yet but thats next on the list. If you have any advice on any of it wether it be how i can get my mpg back or keep it from overheating help me please

1) Have your catalytic converters check @ any local muffler shop.
2) Look through the grill, and check your air condition condensor + Radiator core for derbis & bugs.

What kind of Inake is on this car?

I finally found a mechanic that was worth a damn. He did a gasket check, turned out good. He ran the comp. and said this. "The reason for the overheating is because there is a missing little plastic piece that catches air from under the bumper and sends it through the radiator to cool it. The bad mpg is related to a bad egr valve and an o2 sensor. So im gonna try these problems and see what happens from there. I have a cold air intake, and the catalytic converter has been removed if that is what u mean. Thank you for your post

yup, missing air dam. :thumbsup: