I've never really been able to find a solid answer on this.
Do a bit of highway driving and for the most part it is clear driving but often there is long stretches with snow cover spots.
Would there be any issue driving 100km/h (60ish?mph) with auto 4x4 on or is this too fast.

 

Consider this...

...kinetic energy is: E=m/2 * v2

Where E=Energy
m=mass of the vehicle
v=speed(velocity) squared

It's the square of the speed that increases the energy going double the speed results in four times the energy.
https://www.driverseducationusa.com/...gy%20increases.
this is not yet taking into account the reduced friction of a contaminated road, where contamination can be standing water (aquaplaning) slush (aquaplaning/slippery) snow (slippery) ice (very slippery).
In aviation we consider wet with a factoring of at least 15 % on the stopping distance and 50 - 100 % additional distance for slush and snow. Wet ice accounts for 300 % or 4 times the required stopping distance of a wet runway. It comes close to that with cars, except that on wet ice a car is completely lost as nearly no force can be transmitted to the road at all.
https://www.driverseducationusa.com/...ction-on-cars/

The higher the speed the smaller the ability to transfer a force to the road through the tires.
The higher the speed the shorter the time to see something and react to it.
The higher the speed the longer it takes to slow down.

4x4 is nice to accelerate but when it comes to deceleration or braking it does not help. Then your Blazer can easily become a "puck" on the road like any other vehicle.
It all comes down to road conditions, tires, drivers abilities, traffic when considering a speed to cruise. It needs a lot of experience to judge road conditions and there is always that surprise where water drops from a bride above and freezes a stretch of road beneath, or the road is wet but the curved bridge you enter is suddenly frozen solid.

IMHO you can do 100 km/h (60 mph) but I consider this being high speed in these conditions. Consider this:
100 km/h (60 mph) = 27 m/s (88 feet/s) - along a row of parked vehicles that would be approx. 5 cars in one second!
80 km/h (50 mph) = 22 m/s (72 feet/s) - still about 4 cars
60 km/h (37 mph) = 17 m/s (55 feet/s) - still about 3 long pickups
50 km/h (31 mph) = 14 m/s (45 feet/s) - we could fit 3 cars

Look at some videos with the search for "winter, driving, accidents" and consider the above when you see how long it takes to stop.

We had this writeup in the forum. It was for the older style Blazers without the "AUTO 4x4" but contains a lot of information.
https://blazerforum.com/forum/genera...rmation-88400/

I like 60 km/h (40 mph) in rural winter conditions and main or secondary roads. Ample time to detect changing conditions, reasonable speed to get where you want to with a limited risk. Energy is not so high. 80 km/h (50 mph) on the highway with traffic and changing conditions, depending on the visibility and the weather.

Braking on contaminated roads shows maximum attainable (negative) values around 2 - 2.5 m/s2, while wet roads sustain up to 3.5 m/s2 and a dry road can go well beyond 5 m/s2.
Race cars with slicks reach over 12 m/s2 (a negative, or deceleration of around 1.5 g's or even more).

References for the scientific inclined:
https://rmets.onlinelibrary.wiley.co....1002/met.1285
http://umich.edu/~umtriswt/PDF/SWT-2016-10.pdf
https://www.trafitec.dk/sites/defaul...0behaviour.pdf
https://www.researchgate.net/publica...00000/download

 

More worried about wear and tear on the vehicle not so much stopping distance

 

When in AUTO 4wd, the front right front axle stays engaged; when wheel slippage is detected the transfer case ****s into 4HI. Owner's manual says this can be done at any speed....but seems to me that shifting at 100kph would sure tend to wear-out parts quickly.
I also do not know the parameters for when the transfer case is switched back to 2HI; perhaps a distance traveled with no slippage detected....IDK. But once again doing this at 100kph sure seems like this would be putting stress on parts.....and transfer cases are not cheap.

Using AUTO 4wd seems better to me as this avoids the sliding collar that engages the right front wheel to the front differential; doing this at speed would wear-out that interface quickly.

 

FYI: The acceleration due to gravity, "1 g" is 9.8 m/s^2. So 3.5 m/2^2 is a bit over (1/3)g.

 

Thanks Christine

As long as you go straight and have no slippage at the rear axle you can go in and out of 4HI any time and won't be putting more stress into it than at 10 km/h.
There is nearly no rpm difference between front and rear. That is what put's stress into the drivetrain. AUTO is doing that when it detects a difference between front and rear which means i may put even more stress into the transfer case as if switched on manually.