For the upgrade of offroad lights, there are some considerations.
1. How often do you anticipate using lights other than your headlights? You may consider upgrading to Hella, Cibie', or similar replacement headlights before going full bore on offroad lamps. I'm running the Cibie' Z-beam with 60W low and 100W high. This setup is pretty good, most of the time.

2. For every so many Watts, you'll need to supply so many Amps and I think the alternator is rated at 45 amps. Remember the alternator and battery will have greater loads with more lighting. I have an Optima and will be working in some other alternator when I hook up my accessory lighting.

3. Air resistance: depending on where you mount the lights, you can negatively affectv your mileage. As in the photo responses to your other post, you'll see that Les and I mounted the lights on the front bumper. Others like 89Monty, have their lamps mounted on a roof rack. I'm jealous of the rack <img src="/forums/images/graemlins/baby.gif" alt="" /> !

4. Money: sounds like you'll need to get the truck mechanically reliable before you spend $$ on accessories. Me too!