Well first of all, what do you use your truck for most often?
There are a few types of "positraction" differentials. There are limited slip differentials, lockers and spools. I'm going to guess you don't want a spool!
Limited slip differentials are built similar to open differentials but have clutch packs to control the torque split between the two wheels. If your truck never really sees any offroad use, it is all you really need on road because they still allow the wheels to differentiate under power.
Lockers are a different animal. Most of the work where they lock up to a 50-50 power split while under load and unlock when there is no load present. This allows the wheels to differentiate through a turn as long as you don't have too heavy of a foot on the gas pedal. If you are pressing the gas pedal too hard, for example, turning right from a stop sign or traffic light, you can easily lock up the locker and cause one wheel to be pulled through the turn, causing accelerated tire wear. These are much better for offroad use because if you got in a situation where one wheel was completely off the ground, the other wheel would get power, whereas most limited slip differentials would slip.
If all you want is a limited slip diff, the easiest thing for you to do is to find one in a junkyard and swap the entire axle assembly! This will prevent you from having to re-set the carrier bearing preload and ring gear backlash.
If you want a locker, they make "lunchbox lockers" like the powertrax no-slip that replace the guts of an open differential case so you can install them without removing the carrier and again avoid setting bearing preload and backlash.
If you aren't opposed to getting in that deep with a differential install, or don't mind paying someone else to do it, there are several other options for aftermarket LSD units like Auburn Gear Differentials and full lockers like Detriot lockers, but its debatable as to how much better or stronger they really are.
Last edited by 95_318SLT; 02-26-2010 at 10:29 PM.