Did you run the temps up at the end?
Forgot. what pellet grill is it you have?
I did a 3 beef short ribs yesterday. Decent. GREAT smoke and flavor. But, did not get that nice unctuous meat I usually get. Though these were not cut or marbled well for for smoking. I'd bought them at Bull Valley Farm's Store. Frozen in butcher paper. Ostensibly to cook them for last evening for daughter #1 and myself.
But these were not well suited. Quite honestly had I known how these were cut I'd have saved them for a winter time pressure cooker braze or stew of some sort. They weren't "marbled" as you expect with short ribs. They were more large "striations" of fat layer with very lean meat layer. So, "rendering" meant I turned the "lean" portion in to more of a "jerky" portion