I believe you will find that "Pennzoil"-branded filter will most likely be manufactured by Honeywell/AlliedSignal... IIRC, Honeywell/AlliedSignal owns Fram if I'm not mistaken. It would therefore reason that your Pennzoil-branded filter is similarly constructed as a Fram, and Fram is not/was not an approved oil filter for the Cummins (based on a TSB through Dodge).
While there are other [good] choices besides Fleetguard; Fleetguard poses the least risk of those choices IMO.