I could go into endless details for why I committed to an Eaton Truetrac differential. It all goes back to an engineering publication my father (who designed propulsion systems for the Navy) read back in 1968. I'll spare you that torture. A truetrac differential runs about $700 to $800 just for the unit itself. That's the tip of the iceberg , because it does not accomodate factory style C-clip axle retainment. You are forced to modify the axle with C-clip eliminators or 9" bolt on style end housings. I am currently updating a "how to" thread on building a fully streetable axle with no compromises; full parking brake, ABS retention, and 4 piston caliper compatibility that will deliver over 1000 ft/lb of torque to the street. It will be the only "how to" on the internet that I can find after 8 months of research. It's not going to come cheap though. I have sunk about $3400 into this axle so far.
Kurt