anybody who recomends auburn is losing there mind. they are not rebuildable. eatons are nice but they are too much money IMO. If you want carbon fiber clutches ford sells them for $100 as opposed to $50 for the stock ones.
the factory trac lok with the right clutches will work fine in my opinion and if you ever break it your not out $500. all LS differentials ie trac lok, auburn, eaton are all breakable.
If you ever want to launch on slicks go 31 spline axels. if not your 28's will proably do you fine. this adds to labor if you have abs though as you have to deal with your tone rings and such. at 40k I don't know I would worry about an install kit.
Any mechanic who will not rebuild a trac lok has either not done them that much or something is wrong. they are not complex at all.
Well I did it. Got the 4:10's yesterday, dropped the car off this morning to have them installed . I will def create a new thread on my review of them along with small video clips of some MPH/RPM comparisons. I ended up doing the rebuild kit for the stock diff. Thanks for everyones input!