1. Silverstars or Phillips extreme would be your best start for OEM replacement and DOT approved. Avoid cheap ebay bulbs or blue colored bulbs as they actually decrease usable light output.
An HID bulb in a reflector lens may work for some but personally I would not want to be inconsiderate to any incoming driver. For those who argue that the cut-off is ok and it's not blinding anybody, I invite them to get their headlights properly checked by an optical beamsetter.
2. The best legal and efficient solution would be an aftermarket wiring harness as Aldive has already suggested above. This allows the bulbs to draw power directly from the battery giving you optimum output from whatever bulbs you have. You can purchase the harness pre-made or you can make your own using your own parts. I did the latter and I think it's worth it.
http://www.explorerforum.com/forums/showthread.php?t=266362
3. Aftermarket lenses and reflectors give slightly better output but be wary of quality since a lot of the cheap ones have the lenses yellowing in just a few months. At least one member here, Celly has an aftermarket housing that combines HID and a better housing.
4. The best result and output would be with proper HID retrofits or a custom HID projector housing but check with your local laws. I know that in some places, if your truck did not come oem with projectors-HID then any retrofit or non-oem housing may be illegal.
5. If you go with step 2 above, you can even go with higher wattage bulbs. Arguably some people would say it would discolor the lenses further or burn off the "chrome" like reflector of your oem housing but I know a few people who have gone this way and if the oem housing does get damaged later then the housings should be changed anyway. Granted, higher wattage bulbs may not exactly be street/DOT legal as well, but done properly and conservatively the usable light output would be better.
And the aftermarket harness is also usable with an HID retrofit if you choose to go that way. Not only will it give better light output but it would also prolong the life of the ballast since there would be little current fluctuations becaue of the inline relay.