I have a 2002 hyundai accent gl. 2.5 4cyl. The check engine light is on and stays on. The car drives good as long as the gas tank is full. Once the gas tank drops to half a tank or less it starts missing real bad. I have taken the car to two mechanics and they can't find the problem. I have several codes I got from autozone po442, evap system leak and to lean. Why would the car run good when its full of gas and miss when low in fuel.

That misfire is probably due to an internal (to the tank) fuel system leak.
Inspecting for that leak will require removing the tank from the vehicle.
The P0442 will need hands-on diagnosis.