The TracLok is a limited slip type of differential, or what some folks call a "posi" rearend. It basically splits the power to both wheels when one looses traction, vs. all power going to the one that's spinning with a regular or "open" diff. If you're pulling your boat up a wet ramp with an open axle, one wheel can spin forever and the other one just sits still. With the posi-types like the TracLok, IF one wheel starts to spin, the other side gets some power and hopefully has enough traction to get you up the ramp.
This system uses clutches or discs to still allow some slippage while dividing the power to each side and relieve some stress on the axle shafts. Something like a locker does what the name implies. It "locks" both shafts together to give equal power to both sides. Great for traction, but they need to have a way to unlock when turning a corner or else the outside tire has to slip.
Whether you go with a 4" or 6" lift, you will have to lower the hitch mounting point on your rig. You can use a drop hitch or dropped down style bumper, but that puts alot more leverage on the hitch. You'll need to keep the rear anti-sway bar, too, to help control the truck and trailer when towing. If you don't plan on offfroading very much and want to keep the stock suspension but get a "lifted look", then consider a body lift instead.
