How do I know I'm at top dead center
 

I had skipped the chain while installing the water pump and I need to know how to tell if I'm perfectly on tdc. I lined up the links with all three tick marks on the main chain and turned the crank two revolutions and the tick marks were in the same spots. Is there anything I did wrong? Please help I need to get back on the road soon.

It's perfect but
 

I'm still over heating. The thermostat and water pump have been changed but now I'm still over heating, what things would be causing this? Head gasket? Could the temp sensor do this? Need help soon please

And
 

The radiator and cap are 6 months old.

Think you started on the wrong side of the story here.
I would first verify that the temp gauge is working correct by using a thermo gun and see what temps you have on the hoses to and from the radiator. (fans confirmed working?)

How did the overheating start? Did you do any work on the engine/cooling system before this started?

How thorough were you with burping the coolant system? Could be a bit of air stuck somewhere.