There seem to be some crossed wires here somewhere.
Your truck is fitted with an LSD in the rear and an open diff in the front.
The truetrac is Detroits limited slip diff. This is a good bit of kit using gears instead of clutch plates like the one you have. It also relpaces the standard carrier and is a much stronger beast. There are two types of none switchable lockers. Ones which fit your existing carrier and ones which replace it. Sticking with Detroit these are the ez locker and soft locker in their product line, there are others.
There are pros and cons to both. If you keep your existing carriers then there is no need to regear and mess about with shimming etc. but you loose out on some strength. If you replace the carrier then you have to transfir your ring gear on to the new unit which means more work (probably best laft to someone who knows what they are doing.) but gain strength.
I wouldn't stick an LSD in the back and a locker in the front either unless you are going to use an ARB type which you can switch on and off. You want the locker in the back and the LSD in the front.
Unless you can live with it not going round corners in the wet.
