The specs look good on both. The C-11 might be working harder and thus less MPG and life, perhaps why it had an early rebuild. I am surprised both have 24.5's. Looks like both were started as dump trucks and not road trucks converted to dump trucks.
The CAT engines are expensive to work on, and harder on fuel typically. Are both set up with a buck plate in the back with a pintal and air to the rear of the truck?
What is the money on these trucks? Can you post pictures?