1998 Chevy Lumina EGR code P0401

I have a '98 lumina with a 3.1 v6. For the last 6 months the check engine light has been on. When scanned gives code p0401 - egr- insufficient flow. First thing I did was remove the valve and clean out the ports, code came back. I then replaced the egr valve and map sensor(even though I couldn't find anything wrong with them, just wanted to eliminate ), code came back with in a day of erasing it , I had the intake manifold completely off last month to do a gasket, recleaned the egr passage, clean out the tube running from the exhaust manifold to the egr. Code still comes back. I'm convinced that the computer is either reading it wrong or another sensor is bad. I purchased an auto xray 6000 scan tool, which will be here tomorrow. What sensor readings, info, ect. Should I look at? I've never used a scan tool before