2001 Monte Carlo SS

So I been getting a couple codes lately: P1404 and P0404. Did some research and I tried the post here with unplugging the EGR valve and scanning and clearing the code. Turning off the ignition right after clearing the code and then plugging back in the EGR pigtail. Code came right back after driving a week or so. So then I cleaned the EGR valve and the input tonight. There was actually NO carbon or soot that came out of the valve and the pintle seems to move freely without any hesitation or sticking. Should I have this diagnosed next? Should I just buy an EGR valve? I hate to throw parts at it if its not gonna fix it. Tonight after cleaning the EGR valve and scanning and clearing the code and turning the ignition off right after and then plugging the pigtail back in.....the P1404 code came right back after driving about 5 miles. I'm lost on what to try to next except to let a mechanic diagnose it? Any thoughts or suggestions?

Oh the P1404 doesn't seem to give any symptoms BUT the P0404 gave me some hesitation and rough idle.....if that means anything?

 

OK so an update: The light was on this morning on my drive to work. When I left for home 8 hours later the light was out. It came back on after I left home again for a short drive and then it went out again.....and is currently out. So whatever it is....it comes and goes? I'm sure it was the P1404 code again. Any suggestions?

 

So I got some info on testing the EGR but its too cold out and I'm too busy to be fooling around testing this.....so here is my question: Is it important that I buy an AC/Delco EGR or a Delphi? What if I go with a knock off with like a 10 year or lifetime warranty. How important is it to stick with a name brand on the EGR? I can pick up a knock off for about $30 and a Delphi for about $60. For that small amount its worth it to me to not to have to mess around with this in the cold.

Also I have another problem and I'm not sure if its related to the EGR valve....my gas gauge hasn't moved off full in like 3 days. That is not normal behavior so I'm wondering if the PCM is reading the pintle position as open/closed and its effecting the gas gauge reading? In the past month I have had the following codes: P1404, P0404, P0446, P0440 (purchased Vapor Canister Purge Valve)....the only code that has come back since changing out the Vapor Canister Purge Valve is the P1404 and P0404. So I'm wondering if one of these codes can lead to my gas consumption not being displayed correctly OR if I have something else going on now?

Also before I got this P1404 code I purchased one of ZZP's voltage increase adapters for hooking up to the alternator. This thing wouldn't have messed up my EGR valve in any way would it?