Update**

So for some reason I didnt even think of it, but his two hides are different... and he never uses his warm hide. So I switched them around (put his cool hide on the warm side, vice versa). Boosted the temp up slightly, so that the warm side was between 92-88, cool side between 82-86.

A few hours later, he was out and warming on his rock. I left a large hopper in there on the warm side overnight, and it was gone this morning. And hes still in his favorite hide...on the UTH. So it seems that the issue was hide preference..and the favorite happened to be on the cool end.

So I'm hoping this was the issue, and my next step is getting two identical hides in there. Fingers crossed