Digital is good. Hopefully he'll come around. Let us know how the night-time temps look with the new thermometers. If your temps have been hovering between 75-80 I think organ damage is a lot less likely. You could be looking at a lack of vitamins instead (can sometimes cause twitching/neuro issues), but that's more easily corrected and the worms sound good.
If by grubs you mean superworms, don't feed those. They have a lot of chitin in the exoskeletons and that can cause impaction.

UTH means Under-Tank-Heater. They come in a bunch of different sizes, and are made to stick to the bottom of the tank. For pacs, they should be put on the side since pacs burrow to cool off and having a heat source beneath them can confuse them. I prefer heat pads to lamps just because they allow the frog to self-regulate more. I like having a room just for the reptiles so I can just keep ambient temp 80-82 and not worry about lamps or UTHs except during winter lol.