Okay... I finally decided to just replace the barometric pressure sensor and the EGR boost sensor solenoid. These are the two "gizmos" on the firewall above the EGR valve at the intake (see pictures). The part numbers I could find off the parts I removed are as follows...
Baro sensor: KL47, E1T10372, A 4526
EGR Boost sensor solenoid: K5T49096, BP4Y, 4427
Both of these parts are made by Mitsubishi. Using one of the two links provided by @DrFeelGood
above, I was able to buy the EGR boost sensor solenoid. The one the Doc listed for the baro sensor is actually a MAP sensor that goes in the air intake and is not the correct part for this application. It is likely the same gizmo inside the plastic, but the wrong orifice for the baro sensor needed for the EGR system. I found my Baro sensor on EBAY listed as an OEM part. I had thought I was getting another Mitsubishi part as that's what they had pictured, but it turned out to be manufactured by FAE. I was a little disappointed with that fact, but I will live with it as it is still a new part rather than used.
Wide angle shot of the parts on the fire wall for situational awareness
Close up shot with the Baro on the left and the Boost sensor solenoid on the right
After replacing these two parts and then driving to the parts store to have them clear the codes (I still don't have a code reader), I have now driven 100 miles and the check engine light has stayed off. The interesting thing is that the boost sensor solenoid checked out fine out of the car. It held vacuum as explained earlier in this thread and changed correctly when 12v was applied to the contacts. I didn't test the Baro sensor, as I was just a bit tired of the problem. So I'll never really know what was wrong, but it appears that the issue was with these two sensors on the firewall.
As I stated in an earlier post here, I did see some improvement (check engine light stayed off for a while) with cleaning the EGR probe tube, that did not keep the light off. I feel like it did need to be cleaned though, so I'd likely suggest that as part of this repair that the EGR tube should be cleaned and then those two sensors replaced on the fire wall. I'll be going in tomorrow to get my emissions test as I need to renew my tabs. I'll report back if it stayed off long enough to get to the testing station and if I indeed passed. I'm feeling pretty confident now that I've logged 100 miles though.