I've got nothing against Delvac 1 (in fact I think it is super oil) but Rotella T Synthetic has shown good results in the few analysis that have been posted and it is definitely way cheaper when purchased at Walmart.
I would go with the Rotella T Synthetic.
I've been looking for a 0/5W-40 to run in my '01 Sierra 4x4 with the 5.3L. I was looking to use the new Mobil 1 T&SUV oil until I discovered Rotella T Synthetic. This truck only sees about 10-15K miles/year. At $12.xx/gallon, I think the Rotella is the way to go. It's not a PAO, but I don't think I need the more expensive Mobil1 for no more miles than I drive. Opinions to the contrary?