Tylenol doesn't potentiate anything, although in this case I agree it might be potentiating the retard enzyme.
You can't compare the effects of the same drugs through different ROA and wonder why it doesn't feel the same! Thats like saying "hey I took one half of a sandwich and ate it, then shoved the other half up my butt and it tasted different. What gives? It's the same sandwich??"
My doctor immediately took me off percs and switched to dilaudid because I was taking 3 or 4 10/325s at a time to get pain relief - because of the Tylenol. You're taking way more than that.