I'm no expert, but I don't think that you'll be wearing anything out more than it's already worn out.

[ Thinking out loud... ]

In olden days, you didn't want to leave trucks in 4WD mode because they didn't have clutches, etc., to handle the wheels turning at different speeds for long periods of time. They needed to be able to slip the wheels.

Ever since the days of Audi starting to put 4WD in everything, since the advent of cheap clutch systems for 4WD, I think [but see below!] it's been less of an issue.

AFAIK, the only issue with keeping newer things in 4WD mode is potentially greater tire wear, maybe more noise, and maybe a little worse mileage.

Let's see what the actual experts say... GMC.com:

HIGH-RANGE FOUR WHEEL DRIVE

High-range four-wheel drive, marked as “4↑” on most transfer cases, is designed for use on loose or slippery surfaces. In this setting, the front axle is engaged, and the transfer case then sends power to both the front and rear axles and to all four wheels. 



This mode forces the front and rear axles to spin at the exact same speed. Due to minor tire size differences and track length differences when turning, the front and rear axles can ‘fight’ against each other on high-friction surfaces and results in a condition sometimes known as ‘crow hop’ as tires are forced to slip to the ground.


Since GMC’s transfer cases are designed to be “shifted on the fly,” drivers can shift between high-range two-wheel drive and high-range four-wheel drive without bringing the vehicle to a halt. On electronic transfer cases, an indicator on the selector knob will flash while the shift is being performed and turn solid once it’s fully engaged. For trucks equipped with a manual transfer case, an indicator within the gauge cluster will illuminate.



It’s important to note that high-range four-wheel drive is not intended to be used on dry surfaces or roads with good traction. Doing so may place undue stress on axles, transfer cases, and other drivetrain components which could lead to damage. It’s important to remember to shift out of 4 HI as soon as road conditions improve.

So, they apparently don't have the clutches and smarts that Audis have had for years, and you don't want to leave them in 4WD mode all the time.

HTH!

Best wishes,
Scott.