I don't have a pellet grill, but have learned the hard way. I cooked so many ribs till they were almost charcoal trying to do the 3-2-1 method and not knowing how to check for doneness. That is for full side ribs, and at 225 I think. I cook around 275-300, side ribs are done sometimes at about 3.5 hrs and side ribs at around 3 hrs. I'm not good at probing. Always leaves me with questions. I do the bend test. If you grab that thing half way (or less) along the rack and watch the bend, if it is starting to break apart and flop down to nearly 90 degress, you're done (or overdone). I'm just an amateur, but that's what I do do and been having some real good ribs lately. Keep in mind this is in a drum smoker, not a pellet grill, so your mileage may vary.