All broken rings were top rings. The T shape could be due to odd wear after the rings broke. I'm sure they have been broken for over 10,000 miles. When I first got the truck, it had all of the signs that it had been run at low speeds under light loads a lot, lots of carbon. Well, I like to give it a little gas every once in a while and the ridge was probably low in the cylinder as a result of low speed operation and the rod stretch at the higher rpms was enough for the top ring to contact the ridge.