[updated:LAST EDITED ON 31-Mar-02 AT 12:31 PM (EST)]I have a truetrac in my front axle and I really like it. The truetrac is a limited slip that uses gears instead of clutches to transfer torque over to the wheel with traction. Mine operates smoothly, I can hardly tell its there. However, I don't think its offered for either the 7.5 or 8.8 axle. I put a detroit locker in my 8.8 and I wouldn't say that it's horrible on the street, but you will notice it when it disengages for turns.
Here are some basics. A spinning tire can withstand 0 torque. A standard (open) differential transfers equal torque to both wheels. So if one wheel is spinning the other one recieves the same amount of torque, which is zero, and you don't go anywhere. To combat this limited slips and lockers are used. Lockers usually replace the side and spider gears with a device that prevents differentiation. My detroit for example uses spring loaded drivers that have teeth that mesh when wheel speeds are equal, when turning, the teeth on the outside wheel's driver disengage and this lets that wheel turn faster. The inner wheel remains locked to the power source. After you're through the corner the teeth align again. The engagement and disengament is where noise and poor handling characteristics come from. Limited slips work completely different, they use clutches or gears and they only transfer some of the torque to the wheel with traction. They are smooth and are road friendly but can't compare in strength or function to a full carrier replacement locker.
If you feel that you need the benefits of a locker and are debating between locker and limited slip/posi (they are two terms for the same thing) then I would recommend that you take a ride in a truck that has a locker and see if its something you can live with. Good luck.
-Cope

95 F-150 4x4
4.9L M5OD
Front Truetrac Rear Detroit
3.73 Precision Gears
Warn Premiums
4" Superlift Superunner