My 2003 1500HD 6.0 also came with the pf44. The same truck prior to 2003 came with the larger pf59. The dealer told me that they were using the larger 59's on the 2003 for oil changes, until they got a memo from gm to stop doing it. No one knows why. I will be using the 44's on my truck.
BTW Delco has recently disconitued the 44 and the 46's are now recommended for our trucks!