Well I almost have 'Silver Flash II' running tip top with all my mods -- but as usual, something else happens -- I have been getting an intermittent DTC P0401 EGR Low Efficiency; I stopped and bought a can of cleaner but is it worth it? I found a New Delco EGR Valve on ebay for $70 and went ahead and bought it and cleared the code for now.. and also I popped another code recently for Coolant Temperature Sensor; gauge is reading fine though -- checked the connector .. is that common to go? I went and bought a GM one off ebay for $13 bucks

Do these codes randomly ever mean anything else I should look at? Or anything I could have done to trigger it? I did pull the nosedrive a couple weeks ago for inspect and coupler change, fuel level sensor, intermediate shaft, both O2'* replaced, and Magnaflow CAT install, PCM, and MPS all withing the past couple of months. Checked vacuum lines and all looked excellent and connected.

Gas mileage is averaging 24-26 MPG highway for me as well.

Thanks in advance --
Cale

Your mods sound good so far.
The egr code is not common but some of us have deleted the egr altogether and had the code programmed out.
The coolant code? Which code is it just sensor low level or not reading? Not sure what you meant.
The 2 codes are not related and don't indicate anything seriously wrong with your car at this point.