Although I live in South Louisiana, and it never snows here, we do have a lot of mud, and a lot of rain here, making for some slick roads, from time to time. Most 4x4s has an open differential, so 1 tire bites, and 1 does not. In 4 WD, both front, and rear differentials have 1 tire that pulls. In all wheel drives, a 4 tires pull. In a limited slip differential, both wheels will lock together to pull, as needed, but will allow the outer tire to turn free from the inner tire, in a turn. This allows to outer tire to turn faster, than the inner tire, so that you don't drag 1 of the tires, around a turn. In a spool rear end, both tire turn at the same speed, all of the time, so as you turn, you are dragging 1 tire, every time you make a turn. Most spools are used for drag racing. I have an Eaton truetrac in my 97. It is a limited slip carrier, that works with Helix gears. As 1 tire slipes, the gears engage to apply power to both wheels. My 79 Corvette, has what they called at the time, positive traction. This is a limited slip carrier, that has clutches to lock the tires together as needed. As 1 tire slipes, the other will apply traction so that both tires will bite. All of these differentials have +&- to them. Also in a 4x4 application, the gearing, and carriers need to match from front to rear. Before I installed my truetrac in my 97, I looked at the power trax insert for our differentials. This is a good option for traction issues also. It all depends on what you want to do with your truck. Personally, my truck is a street truck, that never sees off road. I just wanted better street traction. That is what the truetrac gives me. There are more option of course, but a lot of the other options are electronically controlled carriers, controlled by the vehicles ECM.
