[tdangle]

maybe with the upgrades you are driving harder? If you are mainly in the city, those upgrades will only help a little. the OD trans will help on the highway. Also what is your rear gearing? If it is already numerically low (meaning high gearing ratio) you may actually be having to work the motor harder to accelerate and maintain hwy speeds. Years ago I had a Dodge 1/2 ton 318 with 2.94 gearing and a 3 speed auto trans. I changed the rear gears to 3.55 for towing and ended up improving mileage all around.

Good luck and enjoy your truck