Over the phone, that is the answer you will get. Go talk to him in person. If you have spent any money there for servicing they will probably be more helpful. From what I have heard, they have to directly prove that the mods were the cause of the failure. I know people have had good luck at Tower and Airdie, however that is where they purchased the vehicle. A 2-4" lift is not going to cause any major driveline stuff to wear prematurely, except for stuff like bearings and u-joints. Yes you could break an axle, but you could also do that on the street.