Rather than jack stands,
Get your General on a concrete surface, like the garage floor. Get the machine so that you have 6 to 10 feet of open space in front.
Use a floor jack, inline with the machine, and raise the rear wheels about 4" off the floor. Sit in the Driver's seat.
With the AWD switch OFF, start the machine, put the trans in L, and give it a bit of throttle. The rear wheels should begin to turn, and that's all.
Step on the brakes and bring the rear wheels to a stop. Flip the AWD switch to ON. Give it a bit of throttle. The rear wheels should begin to turn. After only about 1/4 turn, the front diff will lock up and the front wheels begin to pull the machine across the floor.
Repeat the process, but put the Trans in R
If, with the AWD switch ON, the front diff engages...then its working as it should.
For the most part, except in a lot of mud or water, where you can see all four wheels spinning, you actually don't really know when the front diff is engaged.
Pirate