car is running to lean will not pass smog.

On these 4.9 liter engines, they have a rally hard time getting passed the NOx part of the test. It may not be too lean, it may be that the engine is too hot, or the EGR valve and control solenoid is not working correctly. Did you get an AC Delco EGR valve that EXACTLY matches the part on your old valve, if not, it WILL NOT WORK. I do Gold Shield Smog Failure Diagnosis and repair in California and deal with the 4.9 V8 Caddy Smog Failures a lot. Your car is complies for the Gold Shield Program in CA and that will provide $600 ($100 deductible ) in help to get your car fixed. Also go to a Gold Shield Smog Station, they are the best Smog Techs for this kind of job. You can call the BAR to find the location of the nearest Gold Shield Smog Shop.

check fuel filter for restriction\fuel injectors for clogging check fuel pump for low pressure report emission numbers hc, co, nox, o2, co2--- at idle hc, co, nox, o2, co2--- under load let us know(post your question again)with this additional info.