What is the recommended synthic oil, mileage intervals for this engine. I have been using Rotella about ever 7K. No problems, but reading some horror stories.

If you use Mobil 1 Delvac Synthetic or one of Amsoil's full synthetic diesel HDEO, and a premium synthetic filter, you can change it once a year or 15,000 miles, whichever comes first. If you also install a bypass filter, you can go 60,000 miles+, provided you have regular used oil analysis (UOA) performed. Go to Amsoil's site and check things out:

AMSOIL ONLINE PRODUCT APPLICATION GUIDE - amsoiloaf.240582952

I have 5 ford f-550's with 6.0 motors in them, they spend more time in the shop than on the road