YF5 is the precursor to California emissions.
YF5 and YF6 can also drive some non-powertrain specific content. For example, at one time no amber lights were allowed to be seen from the rear of the vehicle, so cab high running lights were amber with a black shield to the rear. Although not powertrain related it was convenient to tie those to the RPO so they made it to the correct region(s).
"Custom Trim" doesn't have anything to do with the California stuff. It is the interior trim level that goes with your "Z84" Cheyenne content.
https://www.gmheritagecenter.com/doc...let-Blazer.pdf
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