Mileage
I have a 97 4.0 SOHC, 5 sp auto 4x4, 123K miles. I don't get to drive on the highway too much so I took advantage of an opportunity I had a few weeks ago. From Seattle to Portland and back, plus about 75 miles of in town there, some stop and go. 378 miles total, 15.4 gallons at the same pump and station, 62 MPH while on the highway, 24.5 MPG. Had I straight highway mileage I suspect I would have been in the range of 26-27.
I bought this vehicle on eBay and I've been tinkering with it since. Just when I think I'm getting to the end of my to-do list and can do some fun stuff on it, something else breaks...this weekend, the master power switch for the windows.
I did a Seafoam treatment before I left on a trip this weekend and I notice the difference. It idles much more smoothly, and I think at light throttle the TC is locking up in third at about 25 MPH. About 300 straight highway miles, (edit: ~125 miles or so at 72 MPH, plus a major mountain pass) plus a lot of highway/town mix and about 40 miles round trip on a dirt washboard road at 15 MPH. I fill at the same station and pump every time, I didn't have time today when I got back. Miles on this tank so far, 418, and it's at about 1/4 tank. Whenever I get over 20 I'm pleased. (edit: result 22.2 MPG)
My only modifications are synthetic throughout, Mobil 1 in the motor and Amsoil in the Trans, Transfer case, and diffs.
I have a beefed up valve body to install that I think will help city mileage. Then...if nothing else breaks, I'll probably install an electric fan.
I think I can crack 30 MPG in this (admittedly, at ~62 MPH, slower than Al).