There are two issues here, both related to whether you use it as a truck or as a car with a really big trunk.
The LT (light truck) series tires usually have a higher load range than do the Passenger series. One would expect the tradeoffs to be higher cost and lower carlike qualities such as handling and noise. If you drive around with a bed full of construction materials or a heavy camper and two weeks' worth of hunting and fishing stuff or whatever, it might be worth your while to consider gross weight.
Either series can be had with a variety of tread styles from highway-only to significantly off-roadey. When going on bad roads or none at all, you usually want a blockier, more open tread that looks like it'd dig into mud for traction and fling it out afterwards. Such tires also tend to have tougher, straighter sidewalls so you don't kill 'em on sharp rocks and so forth.
Winter performance, if that matters to you, can be harder to tell just by looking, though if going through deep snow matters to you, a blocky tread sure helps (this from driving both an S-Blazer with mildly SUV'ish passenger tires and a new Dakota that still had its OEM all-terrains in snow last winter -- it made the difference between a churny, squirmy excursion and just another day at the office). Check out the ratings in addition to eyeballing them. Of course, if you deal with serious winter a lot of the time, a set of steel rims and some snow tires might be in order.
The bottom line on the bottom of your truck: yes, there is a difference, but which way you want to go (to engineer is to compromise or specialize) depends on what you mean to do.
Probably most people with pickups and SUVs are fine with a tire in the passenger series and the highway style -- but there are also numerous exceptions, and if you're one of the exceptions you wouldn't want to get stuck (in more than one sense of the word) with a badly wrong tire.
Cheers,
--Joe