Replaced the fuel pump twice. still no pressure. possible air lock or bad relay, or bad regulator for injectors or i'm stumped . what should i check next?

code p 0300 is random misfires and is generally related to fuel and injector problems rather that plugs , coils and wires
Check for fault codes that relate to the EVAP for non venting of the tank, which causes a vacuum in the tank and the fuel pump cannot supply enough fuel to maintain pressure to the injectors
check for a problem fuel pressure regulator that is not keeping the pump running
check for pump relay problem
check for ECM not switching on the pump relay
check for bad grounds on relay , pump pressure regulator

Then your fuel pump is not working, or your fuel filter is blocked. You will probably have to check your fuel pump circuit if you have no fuel pressure in the fuel rail, where the injectors sit. There is a fuse for the pump, usually in the under hood fuse/relay block. That is probably also where the fuel pump relay is located. You should hear or feel this relay click when the ignition key is cycled from off to on. Also, when the key is turned to on, you should hear the fuel pump in the gas tank turn on for about 2 seconds. This will put the pressure in the gas in the fuel rail, for starting the engine. If you don't hear the pump turn on for that 2 second period, it is probably a bad fuel pump. But know the fuse is good first.

It's possible the fuel pressure regulator is not operating properly, or the fuel pump relay is an issue. Slim possibility the fuel pump
wiring you did is a little off. I don't see that you replaced the fuel filter or filters, could be blocking fuel flow to or from fuel pump.

check for a problem fuel pressure regulator
most are wired to the ECM which is connected to the relay for the pump
it works like this
with low / no fuel pressure the regulator completes a circuit to the ECM
that signal is then sent to a relay to start the pump
when full pressure is reached , the regulator signals the ECM and the relay is turned off hence the pump is not continually running when pressure is not required

If you have a way, check the fuel pressure at the fuel pressure regulator. Sounds like there is no fuel pressure. The injectors are controlled by the computer. Check fuse block for bad injector fuses.

Check egr and sensor for egr.

There is a fuel pressure regulator on the fuel rail. It could be bad. To check this pull off the vacuum line and turn the ignition on without trying to start the car. If fuel comes out of the vacuum hose fitting the fuel pressure regulator is bad. Another possibility is a bad fuel pump. Check your fuel preasure. If low or non exisitant replace fuel pump only after checking fuel pressure regulator. Good luck.

Make sure you check the 3" intake hose from the air box to the intake manifold. May be cracked.

Fuel Injectors possible, however the problem may actually be with the Fuel Injector Pressure Regulator.
Before deciding if it is the Fuel Injectors Check this first. This could be clogged or malfunctioning.
The Fuel Injector Pressure Regulator is available at:
(NO! I do not work for either store/company)
Autozone Part #800-315 for around $45.
Advance Auto Part #217-3074 for around $90.
Advance Auto Part #23043 for around $46.
Adavance Auto REBUILD KIT Item #9710 for around $29.
Let me know if this helped, or if you have additional information or questions. Feel free to contact me at FixYa.com!

Try replacing the fuel pump relay. This should fix your problem. Good luck