scan it and see just b/c MIL isnt on doesnt mean it doesnt have a soft code that wont trigger it. i cant believe something causing the truck to do this wouldnt be a hard code but at work ive seen some goofy stuff cause problems before.
your rail pressure will tell you a lot. I had a similar problem once where I could never acheive max rp. In the cold weather it was only worse. low rp, gutless, evetually got to the point where it would die when I threw it into neutral long enough. It turned out to be bad injector tubes. for some people theyre just loose.
I dont have a way to check rail pressure... took it for a drive, it warmed up to 190/200, same out come plus held it to the floor in 3rd gear and it white smoked real bad and died... waited a few sec and it started and drove back to the shop