93 Gl Codes Pulled, Still In The Dark.

I pulled the codes on the Taurus today, I am still in the dark after looking up the codes, my question is should I just replace the parts the codes mention or what, after certain codes mention "signal voltage higher than expected", heres the codes.

336 (twice)- Pressure Feedback EGR (PFE) sensor or EGR Pressure TRansducer (EPT)-signal voltage higher than expected (exhaust pressure high).

521 Power Steering Pressure Switch (PSPS) - circuit switching not detected. (its been leaking for a while, I wonder did this occur because of that)

536 Brake On-Off (BOO) switch- circuit failure or not activated during Engine Run Self-Test.

538 Insufficient RPM change during Dynamic Response Test (Engine Run Self-Test). or
Invalid cyliinder balance test - throttle position movement.
or,
Invalid cylinder identification problems.

My car runs great to me, but It will not pass the first part of emissions inspection (visual) with the SES light on.

Any help would be appreciated.