[xeroinfinity]

your engine misfire is common with GAs. Either caused by the fuel injectors being dirty/clogged or your plugs & wires are bad.
It alone will cause the engine to run Very poorly, and hav little or no power at times.

The fuel level code could be your fuel level device is bad, another common prob with GAs.
IAT-Intake air temp ,, could be bad or hav broken wire(s).

Did Meineke clear those trouble codes?
And did they come back, making it run rough/bad/overheating again?

I would NOT think its a headgasket, at least from what you hav metioned.

When you say it started overheating, how hot did it really get?
Over 230deg?
Are you loosing coolant anywhere?
A simple compression test on each cylinder can be very reliable identiying a headgasket problem.