A few months ago my front passenger brakes started dragging and got really hot..I replaced the caliper and haven't had a problem...yesterday my drivers side started dragging and overheating...just seems odd that both calipers would just go bad within months of each other. I replaced the pads about 6 months ago. Would mud/water ruin calipers like that or is there a problem elsewhere?

 

The drivers side might have been bad all along. Are the Knuckle slides smooth, no pitting? Brakes and bearing tend to get pretty equal usage, so it figures they may wear simularly side to side. Unless, of course, you only drive Nascar tracks.
Mud and water can cause all kinds of issues. Extreme example is the Grand Canyon. You think your XJ is tougher than the planet.