Sayjac, I read the links and interesting. My OP was on my phone so I didn't expand.
My 2000 2500 w/ the 6L had a long filter (I don't recall the PN). My next truck, a '04 2500HD used a long filter too (pretty sure same PN as the 2000). Then partway thru my ownership of it (sold it in the summer of 2010) GM obsoleted/superceded 4 filters & came up w/ a new PN which was a short "baby food jar" size. When I ran out of my stock of long filters, I starting using the WIX equivalent.
When I bought my '11 I noticed that a similarly sized "short" filter (w/ a different thread) was the FF. Researching BITOG & checking the WIX & AC Delco sites, I started using the longer PF63 & WIX equivalent. Then a while back I noticed that GM is specing 2 different filters on basically the same motor.
Tonight I read this: "The current 2013 Traverse owners manual calls for the larger PF63 / PF63E filter." Throw in the "Replace with PF63" notation on a PF48 & you really have to wonder what is going on.
As an aside, I've come across a similar "replace with" note. On my 2011 Polaris Ranger, the FF was 1 PN while the replacement Polaris filter had a different PN & looked slightly different.
All of this is moot as I get 2 years of free oil changes. After that I'll be going back to the PF63s. Heck I may even ask why the different filters are used.