I would go back to IAD and demand them give you something else, even if it’s another Premium Full Size SUV. As far as the oil change, I really don’t think it should matter if you don’t change it within 3 days (the truck won’t die or anything), but that’s Avis’ problem not yours.

After your return, write an email to Avis corporate to get the difference back and possibly more compensation. This is unacceptable.