If it makes you feel any better they have changed and upgraded the diff bracket you've had so much trouble with. It's definitely re-enforced and the washers that you don't appear to have used in this pic aren't necesarry anymore...

http://www.bluebassdesign.com/boonin/diff_bracket_welds/rear_bracket.jpg

Btw, you do know there are supposed to be spacers on the lower towards the back of the truck and the upper towards the front to hold that level right?