I replaced the egr on my 96 LSS and now has intermittant gas odor when driven. Odor goes from faint to jump out its going to explode. No visible fuel leaks have been noticied. Thanks,

No visible leaks on driveway when running?
Probably a leak in the evap system (Evaporative Emission Control System).
This would set a code, is the Service Engine Soon light on?
Your username suggests you are in the salt belt, the fuel filler pipe likes to rust out...I would check that.
Since you were working in the engine compartment, I would check the EVAP solenoid vacuum lines aren't cracked/disconnected, canister, and other components. The system needs to be completely sealed.

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Brando

No apparent fuel leaks when running, this is intermittant, 2/7 days . Replaced EGR for code and low rpm lag which was corrected by egr replacement, however soon there after started to get gas odor in cabin. It is currently not in code, will check evap system, Thanks