I have been looking around and considering a cold air box since the air
boxes on the cummins are restrictive (that is what everyone says, right?).
I came across this part that is approximately 4" in diameter and is sold as
a modification to the current air box.  You cut a 4" hole in the bottom of
the current box and the hard plastic tube fits into the hole and the other
end is done near the front bumper; thus, cold air is rushed into the air
box.  The company I saw this advertised wanted $129 for this simple
modification.  Well, I spent $4 at Lowes for a 10 foot, 4" diameter piece of
tubing that looks exactly like that of the $129 part.  I put that in and ran
the other end down to the front bumper.  Not sure if it is improving
anything, maybe dropping my EGTs a little, but it is too early to tell.
Next I'm considering a full flow through muffler, but I can't make one of
those...

Bob
2003 R3500