As the title says. The engine probably has about 50k miles since the rebuild and doesn't leak or use any measurable amount of oil between changes. A little spooky actually, considering how much it used to use. Right now I run Shell Rotella 15W-40 and the powerstroke style oversize filter. I read some say rotella isn't a good choice for the IDI, but other than high consumption, I'm couldn't find any other reason during my forum search. I have no plans to sell the truck and wonder if the better oil is worth the cost. Even 0.5mpg increase would theoretically be worth it. I'm also using it as a daily for a short commute, and wonder if the cold performance of synthetic might help reduce the higher wear & tear per mile during the warmup cycle (yeah, it's my baby...). So is it worth the change over? Or should I just stick to dino and increase the change interval?