According to what I read in the datasheet, at 103C the max output is 10A. That means to me you're doing something wrong. If you've got this thing mounted to the case made of metal you've probably have a good enough heat sink since it looks like it's operating at near max current. It doesn't specifiy the size or type of heat sink though I think it's necessary.

Me thinks, and I'm very often wrong, you might oughta look at mounting, wiring or assembly to find your excess draw. I'd also like to see your schematic if that's possible.