The 300-something number is irrelevant. If you've had the truck since new, check your service records. If you've never had the brakes flushed, its overdue for it. If you don't want to spend the $100 to have a brake flush performed, then you should have someone show you how to do it yourself (or with a helper). You can get a service manual and teach yourself, but it really helps to have someone show you how to do it - and its easier with 2 people.
I suspect that most people just ignore such basic maintenance and some then come on here to complain when their anti-lock braking systems require expensive repairs and bash the brand.