98 4500 with 229k. Was getting 18 around town to 26 when towing the 1500kg camper over hills. 23 when driving into head wind.
New CAT back sports exhaust with added hot dog to add some quiet but still noisier than old.
Now 16 around town. 18 when towing. 20 when towing hills.
Car feels like I have added two cylinders. Revs to redline way too quickly so I have to take care to keep it below 3000.
Best $900 investment ever. Wish I did it before last years half loop as I would have spent way less on fuel and had better chance to optimise fuel cost because stops could be further a part.