Hi Jim, No doubt, your truck must have a oil change reminder, in that
an idiot light comes on at the pre-determined mileage? Then, when you
change oil, you reset this feature, and again, it will light when a
pre-determined number of miles passes on the odometer.
I believe knowing that you do indeed have full synthetic lube in at
least your rear axle will be a plus. Especially for towing, heavy duty
use, and using your vehicle in temperature extremes.
I've heard many standard gear oil lubes offer little protection for the
first few miles when the temps plummet well below zero.
This no doubt is what the factory recommends.
Im sure, you'd have the ability to change your oil sooner if you wish.
Keeping a log book/note book of what services you do to your vehicle is
always a good idea (I do). Not only for oil changes, but when other
services are performed, like coolant/fluid changes, belts, hoses, plugs,
etc., and any mods, or upgrades you may perform.
You made no mentiom what brand, or model this truck is? May I ask?
Wish you best of luck with your new purchase, Mark