OK, lets try this, I had an old ranger that I abused it mercilously. In a quarter million miles, I know I changed the oil 5 times. We took the 2.9 apart, could see the cross hatches in the cylinders, absolutely no sludge anywhere. Using your own logic, that means the 10w30 dino motorcraft oil was just as good as your amsoil, right?
I know this is an old post, but you're saying you changed the oil in this thing on average every 50k miles? Hard to believe......before using Amsoil synthetics for the extended drain intervals, I couldn't go 5 or 6k miles without the oil turning watery and black. And the vehicle was in decent shape; meaning it didn't smoke, didn't leak, didn't burn, didn't knock, etc.
26K?? dang thats some strong oil there to have a report like that...