This is a touchy subject. I'd run Rotella specifically since its ZDDP level is still above other gasser oils. Not in the 1200 ppm range, but around 1000ppm's. That's still good for the 4.9...but I wouldn't run it with night time winter temps in the 20's without a block heater. The 4.9 has exhibited a much harder time getting oil up to the lifters and I've read several posts concerning how they love to eat oil pumps.

There is also a lot more detergents in diesel rated oil, whether it be Rotella, Delo or other brand. Check out Bobistheoilguy.com forum for more info. If there isn't any wrong with your truck now, I'd stick with either Dino Pennzoil or Quaker State Defy. Pennz has higher levels of ZDDP and Moly, and the Defy has higher ZDDP for added wear protection in older vehicles and plenty for properly broke-in flat tappet cam engines. I also believe it is Synthetic blend as well. 5 quarts last year was $14. I'm unsure of its price now. Its still a safer alternative to running 15w-40 and cheaper than Rotella.

Edit: Pennzoil has the higher number of ZDDP in the newest class of API SN rated motor oil, with the certified API Starbust on the container.
If I have provided erroneous info regarding Pennzoil, could someone post the new info regarding the Moly and ZDDP level. Thanks, Matthew