2003 Wrangler x

I was wondering if it came standard with limited slip on all models or if it is model specific or has to have been ordered specifically?

Model specific, and needed to be ordered. You can tell if you have limited slip by jacking up the rear end, putting it in neutral (front wheels chocked of course) and turning one of the rear wheels. If the opposite side turns backwards, you have an open diff. If it turns in the same direction, it's limited slip.

If it's open and you'd like to upgrade, there are lots of options out there to do so.

Hope that helps....