Running a CAT filter on the OEM mount is not usually recommended because they usually don't provide water separation. But one of the filters at the lift pump may be for water separation. Still, I don't think you can beat a Racor coalescing filter on the OEM mount.
Sorry, I don't know anything about your lift pump/filter setup. As above, some allow pass-through (sounds like yours, since you ran it). You might want to fix that up when you can since it may be a little hard on the CP3 pump, and you don't know how long it's been that way.
And, as above, it should just spin off (just turn it the correct way!).
2004.5 Silverado 3500 SRW 4x4, D/A (LLY), Ext. Cab, Long Bed
engineer837 aux rad, TxC CAI, LBZ MP, Scangauge II, Nicktane aux filter head, KD lift pump, 2008 PS pump, 2011 hydroboost, Frederico Swaybars, Rancho 9000XL, Torklift StableLoads, BFG AT/KO2, Lance 835 Camper often in the bed.