I had the same problem about a year ago. Fill plug on mine had a allen wrench type hole that was completely stripped out. I was able to remove it by heating the area up with a propane torch and used a dremel tool to put a notch in the inner part of the plug so I could use a hammer and chiesl to get it to turn out. Heat was the key for me. I was stupid enough to remove the drain plug first... idiot move... now I was stuck in the garage and had to get that fill plug out. I had an old plug from my Jeep Cheerokee that was shaped like a nut so you could put a socket on it that I used to replace the original style. Don't know if you could find that type at NAPA or at a junk yard.
Hope this helps... I know the feeling.
Chuck
Attention: TDR Forum Junkies 
When I bought my 02 I had the dealer completely go through it and replace ALL of the fluids etc as part of the deal. Truck has been flawless but when I went to change the transfer case fluid I think the tech used a AIR WRENCH to tighten the plugs. The inside is stripped a little and they will NOT BUDGE!! They are so tight. Took it down to the Lube place to see if they could get it loose from a pit. 2 big Guys with all their weight could not get it broke loose. ANy clues on how I am supposed to get these plugs out????
