Misfire

Instead of replacing the injectors, use some high quality cleaner. BG44K or SEA FOAM or BG44K. They cost about $20 a can and you should run 2 cans. You might have to go to a service station to get the BG, (which is better in my opinion) or sea foam can be acquired at your local parts store. After you run 2 cans and then you will have to change the oil as the cleaner works so well that the oil ends up dirty from deposits and sludge.
As far as the O2 sensor, if you have never changed it you might want to. It is one of the biggest influences on MPG in a vehicle.

Misfiring can be due to various factors and it might not be the injectors. Were the spark plugs and related components checked?
Was anhtyin done prior to this occurring?
Any other trouble codes apart from misfiring?

This is everything I have done, replaced a head gasket, new timing belt, new plugs, complete tune-up, replaced 02 sensors. I had a diagnostic and found out the 02 sensors needed replaced, i have done that now the only code i am getting is for a misfire, i was told no specific one just coming up as a misfire. I figured the next logical step would be to replace the fuel injector or maybe the camshaft position sensor, the coil pack also came to mind, I don't want to keep spending a bunch of money on the road of trouble shooting.

If you don't diagnose the problem and keep changing components, you are going to waste a lot of money on unwarranted repairs/replacement.

Things you should start with would be :

1. Fuel pressure.
2. Engine compression.
3. Valve clearances.

I had a blown head gasket that is why that was replaced, while that was being replaced we noticed that the timing belt was in pretty bad shape, hence, changed that also, was due for a tune-up. Diagnostic showed there was bad 02 sensors that is why those were replaced. Fuel pressure, engine compression and valve clearances were checked and all are fine. The diagnostic shows that I am getting a misfire code, that is what I am now addressing. Trying to keep spending at a minimum but the logical solution appears to be the fuel injector, camshaft position sensor, or coil pack. I was hoping that someone else possibly knew more than me!

The injector can be tested with a circuit lit or a multi-meter. It will turn on the light when it clicks or it should be getting 12 volts.

The coil pack feed line can be tested to make sure it is getting 12 volts.

The camshaft position sensor would be about one of last thins to be suspect in a misfire situation.

If the backfire comes through into intake is is running lean and if it comes through into exhaust it is too rich.

We cannot guess and tell you what is wrong. Those that I mentioned are possible causes for engine misfire.

Since timing belt was replaced, hae you checked the igniton timing? Wrong timing belt installation can result in improper ignition timing and misfiring.

Have the ignition coils tested. Look out for signs of arcing at the ignition coils.