The 3500 we have has a scored cylinder (#6). I've talked with Dodge (tried) and Cummins. The Cummins rep (Dodge OEM rep) said that it was probably caused by my using Delvac oil after the first oil change and periodic use of K&N air filter. I know several people who use both and use their trucks harder than mine (in TN) and have had no problems. Anyone else heard this? Is this guy just trying to pass the buck (the truck has 140K on it)? I've talked to both Mobil and K&N and their response is make the guy put it in writing.

Exactly, get it on paper.

I think that THe cummins rep just dosn't want to take resposiblity. The few dodge trucks that we get into our shop we use devac 15w-40 and never had any problems with them.

This is probably a few years too late, but scorings on the cylinder wall especially on the #6 seems to be caused by broken Wrist Pin clip.
While lubrication of any components are very important, K&N filter or Delvac oil won't induce Wrist Pin clip failures.
Should be covered by any warranty that coveres lubricated internal engine components.
If the cause of the scoring was due to a bad motor oil, all the cylinders will have same type of damages.

...and on the subject of oil, as long as it meets or exceeds the manufacturer's recommendations, they can't say spit about which oil you used.