I'm going to do a rear brake job on my '97 Bravada. I was wondering if change the rear calipers do I need to bleed all wheels or just the Caliper(s) I change?

 

At the very least, the rear. I would consider bleeding the entire system to remove all of the old brake fluid, flushing the system until you get clear fluid out at each wheel. Start at the passenger rear, then driver rear, passenger front, and driver front last (order from longest distance to the master cylinder to the shortest). Make sure to keep the master cylinder full!

As brake fluid ages, it absorbs moisture which can hinder its ability to withstand heat. If you are already going to be doing 2 wheels, it isn't that much more to do all 4!

 

Thanks for the info.