[oldspowered67C10]

The Eaton tru-trac isnt a locker, its a gear type limited slip(google torsen for more info), its really smooth and wont usually ever wear out but is really better suited for the street. My experience with the tru-trac is that in the dirt its not that great, if one tire comes off the ground or totally loses traction it acts like a open diff and you need to apply the brakes a bit to get the tire w/ traction to move.
The eaton posi-traction isnt a locker either, its a clutch type limited slip. It works well for street and dirt but it will wear out eventually, may need to be rebuilt and will not completely lock the axles together. The Auburn is essentially the same thing but uses cones rather than clutches, some people like them, some dont, never had one myself so cant say for sure how good it is.
The eaton locker is a real locker, it actually locks the 2 axles together. Its the absolute best for the dirt and is practically indestructable but sometimes itll do funny stuff on the street like pop and steer the vehicle into the next lane although thats more of a problem in short wheel base vehicle like Jeeps.
For a truck that sees mostly off road, the locker is the way to go but for a mostly steet used vehicle that is used off road just sometimes the Id recommend the posi-traction.