Just gonna put my input on this topic since I actually own one of these trucks. There is no paperwork that was signed or needed to be signed about any maintenance on the engine. The owners manual does state basic maintenance that should be done just like every other manual I have gotten with a vehicle. As far as the filter needing to be drained at what ever milage, this will more then likely depend on the quality of fuel used.
In my opinion this is a much better engine then the 6.0
I don't dislike chevy nor dodge this was a better styled truck with all the power we needed.
There is plenty of good info about this engine out in the web Joediesel on youtube is a great source watch his videos.
Test drive the trucks if you are really serious wait till all the engines are out and test drive them all and then make a decision.