It's getting to be time to upgrade my differentials. I'm looking into the options I have. As you can see in the pic the stock 95 Tracker rear axle are not tough enough. Pulled these the other day, one broken and one twisted. I have a Ford 9" housing and axles available. This is most likely the route I will be heading for both front(via a customized to fit it's 9") and rear.
 I'm somewhat of a purist and I'd like to keep representing the Zuki nation on the trail as well as I can.
Is there any other option for the rear end that would have larger/more splines that would handle more abuse? Did the XL7 or GV come with heavier rears? The wider track is not a problem as I am already using 2" spacers in the back.

Try the search function.   

http://www.zukiworld.com/forum/suzuki-grand-vitara-vitara-chevy-tracker-(gen-2-platform)-1999-2005/has-anyone-put-a-xl7-rear-axle-in-a-gv/msg142780/#msg142780

Thank you for pointing me in the right direction!

Does anyone know the difference in diameter between the tracker and xl7 axle shafts?

The axles in my 2002 Tracker are beefier throughout the shaft except for the last 6 inches where it tapers down to the splined ends that slip into the diff side gears.

Appears to me Suzuki designed the axles to be the fusible link in the drive train.  Axles are less expensive and easier to replace than blown differentials.

I fit a Grand Vitara rear in mine and all GV front as well with new arms