Replaced just about everything Ac won't work

If you have a restriction in the evap. core the low side would have the pressure drop. Have you put the correct full charge in it and tried it? Sometimes the depressor in the end of your hose doesn't press down on the shraeder core in the service port enough to read correcly. What does it read on your high side gauge with the system off? Both sides should be equal without the compressor running. If it has a restriction it would be between the compressor [rv2?] and the high side port, in the condenser, to cause a drop in the high side.