Cool truck, man.
The 2.8L V6 is a robust engine, and will fetch you decent MPG's on the highway in 5th.
Do you know what gearing you have? If it's stock gearing, 3.55 or 3.73, it'll be fine and plenty good for mixed highway and offroad use. Minor hauling of firewood will be fine.
To keep your MPG up, just keep your truck healthy and with new fluids, clean, free of excess weight, and properly inflated tires to 32-38 psi. An easy throttle technique is the next best thing to good economy.
Pretend the is an egg under your foot. No stomping of the gas pedal; easy acceleration.
If you ride bikes, throttle technique is huge. Cranking your wrist means a bike will go out from under you.