Here's an oil question for you guys with the 7.3. Mine is due for a change within the next 100 or so miles. I generally run Rotella T 15w/40 in 'er. I was at Auto Zone last night (window shopping) and noticed there are serveal different oils available for the truck. What do most of you run (manufacturer and type)? There were GTX, Rotella T, Mobil, Chevron, etc. What should I get? I noticed they were all about the same price.