Which motor oil to use after in frame?

[Waterloo]

I was at the shop getting the list together for the in-frame on my 2008 ProStar with the 600hp ISX CM-871 with @m*m^2, I use the Fleetguard Oil Filter LF9009, oil is still "visually" clean at 12,000 miles...

My serviceman asked me what kind of oil I want in the truck when it is completed. I told him Shell Rotella regular dino, as it has the proper additives that the motor needs. Now my question, stick with the Shell or switch oils? Not so much for the name brand but additive package. And I am not interested in going full synthetic, that stuff is just to costly and I do not like to go longer than 15,000 miles between oil changes. The truck is getting a brand new head from Cummins, and brand new cams, along with the full monty internally liners, rods, mains, bearings, pistons, etc...

Is there something out there with a better, or more complete additive package that I should be looking at? I also like to use the gear oil that Rawze suggests using, http://www.amazon.com/gp/product/B000M8R...detailpage

As far as I can tell, by old records from previous owners I found at Speedco, the truck has used Shell Rotella most of its life.

Any thoughts?