the bulbs are H6054 (6"x7"), you won't be able to just buy the bulbs because the stock headlights in your truck are sealed beam. this means in order to upgrade your lights, you either have to buy a conversion kit or just find a sealed beam that offers better lights.
the conversion kits run from like $10-100+ dollars for the pair...from what i've heard/learned, you pretty much get what you pay for so be a little weary.
for the straight sealed beam lights, silverstars are said to be pretty amazing, for a sealed beam...i've used them in the past and they are far better than the standard halogen bulb for sure.