Nissan Repair: 1996Nissan 3.0l auto 4x4 pickup, kn airfilter, synthetic grease

Question
I recently purchased this truck and I can't believe what a pig it is on gas. Urban travel about 10mpg(imperial gallon) and 16mpg(imperial gallon) on the highway. I put new plugs in it, changed engine oil to synthetic, changed all lubricants in the drivetrain to amsoil synthetic, put in a new KN airfilter. It still is a pig on gas. Is this normal for this model. It is the XE kingcab model. The truck starts well, runs well. I also had the front hubs lubricated as per specs with synthetic grease. any ideas?

Answer
Hi Harry,

Make sure your not running in four wheel drive. My Navigator gets about that and it's a 7200 pound four wheel drive that I do not baby. Also, make sure is shifting. I mean, there could be an issue with it not making 4th gear. I imagine you should be getting at least 20 on the highway.