Mine is straight with no curve. No one ever did any custom work on this truck so I believe the system that's on it now is pretty much a copy of whatever was on it before.
Factory Assembly Manual diagrams appear to show a straight pipe for 3100.
3105, 06, 07, 16 curves slightly to the driver side under the frame rail, exiting under the frame rail and a few inches beyond the end of it.
3102, 03, 04, 12 curves slightly toward driver side a couple inches past the edge of the frame rail
I just went out and looked at mine. There is a very slight downward bend. When standing up and looking at it, its hard to tell that it curves. I had to get under to see it. It seems its just enough for the tip to be below the bottom edge of the bumper
