Welcome to the machine. You have probely been told read the TM's and all you can find. Check all lubes/ fluids before you drive it home. Add good fuel additive for lube and cetane boost. Run through the gears starting second low through 5 low then pull / juggile the transfer lever to high and place it in 4 high then 5 high and you should be crusing. Shift at almost redline 2500 and don't lug these machines.
Once you get the feel of your machine and ground terrain you will find what works best for the truck. Here in Fl that is flat I shift 2 low 2 high then 3,4,5 high and will walk the dog and leave outher Deuces behind cause they have to make one more shift. Look at ground speed chart for each gear on the dash and you will see what I am talking about.
First gear is a deep reduction and is use in soft terrain that steals the power. You leave it in that gear and walk out of the soft stuff at a midrange rpm then when the ground is right you can come out of first and be on your way.
No matter what is said allways do what is the easeyest on the truck clutch/ drivetrain.
Most important be careful with the 13500lb you will be pushing down the road. Figure the red light is allways going to change red and drive it like it has no brakes letting off the fuel early and allways looking for a bail out spot. Better to take out a tree than a family of four.