> #1 What is a GMC5575425 filter? This is a GM part#. The PF4 is an AC/Delco part#, as is PF25, PF35, etc. I work at a multi-make dealership, among them medium-duty GMC. The AC/Delco filters in our inventory are under the (longer) GM part#s. While I don't (or try not to) have an opinion about filters, I DO have one about Baldwin filters! Mike Ioanes