2003 Durango 4.7 4X4
I ordered the Y-Pipe (10778) and it arrived last week. I scheduled an appointment with my exhaust guy to have it installed. Several hours after dropping it off I received a call telling me that the part was not going to work. Apparently the stock pipes from the manifold are more like 2" (maybe slightly bigger) and 2.5" going into the CAT. The 10778 is 2.5 in and 3 out, wrong Y-Pipe.
My guy left the truck on the rack so I could see for myself later that day. The Y-Pipe was definitely too big. Modification and fitment would not have been practical or beneficial. The frame was in the way so very little room to fit this 10778 Y-Pipe.
Was debating to get a different Y-Pipe, but what I noticed after looking at it for myself, was that transition of the pipes from the manifold into the stock Y-Pipe didn't look restrictive at all? The pipes maintained their ~2" diameter into the stock Y-Pipe and then transition into 2.5" out. I've concluded that the exhaust flow is as good as it's going to get without increasing pipe diameter from the manifold back. Leaving it alone for now.
Just thought I would pass this along in case any 4.7 Gen 1 owners are thinking of doing this upgrade. Check the pipes for yourself first to see what you have.