I've recently purchased a 96' 4Runner 2.7L 4Cyl 4WD, it's a five speed with 150000 miles on the motor. When I first got the truck I put new plugs, wires, K& N drop-in filter, a header and full exhaust system (minus the cat.). I also replaced the stock wheels and tires with rims and tires, P265/65/R17's. The new tires are about 2-3 inches taller and quite a bit wider than the origioinal rubber. I noticed right off the get go that I wasn't getting mileage I knew Runners were supposedly getting. I went through about three tanks with the truck bone stock and I got around 15MPG. Even after all of my mods, including the exhaust system(the exhaust manifold was split in two) I am still getting about 15 MPG. I have gotten mixed advice on what may be penalizing me on mileage. My only guesses would be the MAF sensor, O2 sensor, or timing. I can only assume the chain was changed at the schedualed time(90,000?). I plan to put a chain in some time this summer but I am hurting with fuel costs these days. Oh one more thing, I recently took a trip from Helena, Montana to Moab, Utah with four adults in the vehicle and a full load of camping gear and got an average of 22.3 MPG. Any advice you can give me would be greatly appreciated.