technical discussion.. why are the rear diff's failing?

This is a question for all you smart guys out there. Why are the rear diff's failing. What is it about the design of the Titan's rear diff that is making it failing?

I myself think that it is too little. The Titan makes good power and when I look at all the stuff underneath my truck everything is huge except for the rear diff.... it is puny!

I also am thinking of going to a Detroit Truetrac just so I could avoid my rear diff from failing on me. But will this correct the problem? I don't think it will completely as the Diff will still be the same size.

My Titan has never had problems. When I am cruising offroad in 4x4 mode, I put her in third gear... when I towed a 6000 lb trailer accross the country from NH all the way to Nevada I put her in tow mode and 4th gear and she performed like a champ. Sometimes I forgot I even had a trailer back there.

I have the BT package and 4x4, and from what I have been reading, rear diff problems happen most often with:
1) lifted trucks
2) when 4x4 offroading
3) if you have BT package
4) when you tow a lot.
5) occurs about the 50k mark.

Well I done numbers 1-4 and no problems yet, but as of right now my truck only has $30k miles on her. I am kinda worried about that 50k mark.. but I also love my truck and don't want to get rid of her. I guess I just want some input on what I can do to prevent the rear diff from blowing up.... or if I get the Detroit Truetrac, will eliminate the problem or it is basically just a bandaid.