I got the PO172 first then a few days later the PO440. I have replaced the purge solenoid and front oxygen sensor. Anyone have this problem? Any suggestions?

Since there is only one oxygen sensor before the catalytic converter, it really could be either bank of the engine. I would say the 2 are definitely related. You didn't , by any chance, over fill the gas tank recently did you? Could be that the vapor canister is over saturated with fuel and every time it goes to purge it sucks raw fuel into the engine causing both codes. Does your fuel gage work properly? If it is constantly showing 1/2 to 3/4 of a tank that would tell the ecm it was ok to test the evap system before it is low enough to safely do so, drawing raw fuel into the engine. I would take a close look at the vapor canister for any signs of raw, liquid fuel.

Actually I got it confused: I got the 440 code first and then a few days later I got the 172. Previously I had the 172 first and then the 440. Also, I failed to mention that I had the car inspected a few days before the 440 code came on. Anyway what I think happened: The 440 was triggered by the inspection and the 172 has been an intermittent reoccurring problem that happened to coincide with the 440. I took the car to a Chevy dealer and told the service manager my problem. He then printed out a technical service bulletin that said the MiL for po172 without any drive ability issues meant that the PCM needed to be recalibrate. They re calibrated the PCM and so far so good. I don't remember what year the service bulletin was issued, but I think that it referred to years 99 and before as being problematic.