BDS is what I would recommend. They make a well engineered 4" lift that has progressive rate front coils that are side specific. I had a RevTech on my 2010 and it was harsh riding and noisy.
http://bds-suspension.com/product?ma=2&mo=83&ty=1&yr=2013-2015
I have the following 4" Kit with Fox Shocks, and a 2" rear lift block that give the truck a leveled stance on my 2014. I also have Air Lift air bags as well in the rear.
Base Kit Id 696H
View attachment 92635View attachment 92636View attachment 92637
If the dealer sells the truck with the lift I would expect them to warranty it at that dealer. But you might run it to issues at another dealer. I myself have never had a denial of warranty with any of my lifted trucks. The biggest lift I have had was 4.5" and 35" tires. I have had tie road ends, u-joints and etc replaced under warranty. I am sure someone will pipe in here and tell you how they were denied and why would you ever want to mess with the factory look. I understand and TDR use to be a good place for information about this stuff, but you might find more of what your looking for on the Cummins Forum now.
http://www.cumminsforum.com/forum/
Chris
Alaska