[olopezm]

Disconnecting the battery erased all codes in the PCM but since the problem hasn't likely been fixed the CEL came on again.

I would make sure your battery is OK first. Even when the car starts, a battery going out or low on charge can cause weird problems. You can have it tested at any autoparts store.

The EVAP code is more like a general malfunction and not necessarily a vacuum leak. I would make sure all connectors are OK including the PCM connector and wiring.

The EGR troubleshoot is a bit more complicated with the electric EGR valve installed on GM cars. Again I would make sure all connectors and wiring are OK.

Oscar.