A few more tips on engaging 4x4:
As everyone pointed out you can engage 4H while moving up to about 60mph, but it seem to engage quicker around 20 – 25mph. At least this is what I have noticed.
You can lock the transfer case while moving. You don’t need to be stopped and in neutral. If it does not engage while stopped and in neutral then you need to start moving to get the gears to line up.
For 4L you must first be in 4H and then stopped and in neutral. You cannot go form 2H to 4L directly. It’s 2H to 4H to 4L. Wait for it to engage, lights stop flashing, before you put it back into drive. If you put it into drive before it’s engaged you will grind the gears. If it does not engage 4L after 10 – 20 seconds, turn the switch back to 4H, put the truck into drive or reverse and roll a few feet. Stop the truck and put it back into neutral, turn the dial to 4L again and wait for it to engage. Repeat this until it engages. Again, don’t try and drive off while the 4L light is flashing as you will grind the gears.
Say you come out and it snowed 12 inches and you were in 2H when you parked. Or you are in 2H and got your self stuck. You can try engaging 4H while stopped from neutral. Put the truck into neutral and then switch from 2H to 4H. It might engage. I say might because about 6 out of 10 times it will engage but not always. Just depends on how the gears are lined up. If it does engage just pop it into gear and off you go. If it does not engage it depends on your situation. If you are not stuck then you can just put it in gear and go. It will engage once you start moving. If you are stuck then that’s a different process.
If you are stuck and trying to get into 4H using neutral and it does not engage, while still stopped and in neutral switch back to 2H. Put it into drive and try and ease the truck forward or backwards just a bit. Try truing the steering wheel back and forth while doing this. Try to avoid spinning the tires we are just trying to get the gears to line up so nice an easy. Stop and again go into neutral and try switching 2H to 4H and seeing if it will engage. If not keep trying. Just be cautious, you don’t want to be half engaged in 4H, lights still blinking, and gun the truck. You may get a very harsh engagement!