I had a 98 Bonneville with a 3800 I used to average 27-28 MPG mixed driving. I put over 270,000 trouble free miles on it.
I believe in that time I did normal maintenance water pump and I had added a transmission cooler. I should have kept the damn thing as a daily driver. I gave it away to a friend of mine who needed a car. 330,000 and still going.
Here it is at my former place of work. 3480 on the trucks scales with a full tank of gas.
