You are assumimg the codes means to change a part...codes are system activated , not part specific.
An EGR code seldom is remedied by changing an EGR valve...but futher testing of the EGR SYSTEM will find the cause of the fault in the system.
And checking codes in the actual modules is best b/c they are often coupled up with other codes which helps pinpoint the cause of failure.

Also, on your chassis , an OVP relay can cause all kinds of codes b/c it is power feed for the modules, along with the wire harness issues.

Changing parts b/c of a code will bankrupt you real fast. Find the cause.
The OVP relay had a modification change and as I stated , I would see if that part has the new part # on it before I changed anything. And look for cracking wire insulation.
If you already ordered a CPS, go for it..but don't be surprised to find it not to be the conclusive fault. And this is not to imply that the CPS is not the cause of the fault.

Get the HFM codes..you will find much more info by going to the other modules...and you will have the tool for further issues, as that chassis is the last one with owner access Flash Formated codes ....[ OBD1]

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A Dalton