I have the exact same problem. CEL when driving around town, goes off on the freeway. Did the paperclip trick to get the code and its the EGR but it sounds like pinpointing the problem can take a while. Let me know if you find anything.
EGR regulator is an easy fix for CEL if it fails and easy to test. I got lucky and this was what cleared mine. Green top or blue top?
(I know, I know, figure out the Search feature). I'm assuming a few things - that it's the EGR port that's clogged - as I had both O2 sensors and the EGR regulator replaced when I bought the vehicle. Managed to pass smog as the freeway drive up to the DMV cleared the CEL so I found a smog shop and got it immediately checked. I take it I should have the EGR swapped out for a more current version?