http://www.cadillacforums.com/forums/showthread.php?t=62998

a 9 inch rear. whoa momma.

"Beefy" would be an understatement. I'll bet that empty housing alone weighs more than 50 lbs, even in aluminum. The new '06 V rear end supposedly has a larger 9" ring gear and a beefier case. Only time will tell if it's a valid factory solution. I haven't heard of any '06 owners having diff problems yet, but then again, they've only been out a few months.

http://www.cadillacfaq.com/faq/answers/pdf/t56-06.pdf

This is info on the upgrades to the T56, but read the second paragraph titled "32 spline output shaft" for details on the upgraded diff.

If I had an issue with my diff I could see the need but mine is fine.