The rear ends work harder than the motor. With regular oil they are recomended to change at 100,000 miles. Full synthetic is 250,000 miles. I've known folks to just replace oil filters and never change the engine oil. These service due date are just playing it safe. imho. No need to hit the panic switch when the due date is near. As long as the oil remains slicker than owl

thats all that matters. Like donut says.. Just give her a onceover and get in and go. That's one of the bene's of being a company driver. The headace belongs to someone else.