In HI range, the automatic has 4 gears, and in 4th gear you can maybe get to 100 mph.
In LO range, the automatic has 4 gears, BUT the gear ratios are much lower, therefore meaning that in 4th gear you will only get a top end of about 45 mph.
When you use LO range, I would suggest to NOT leave your gear selector in 1st gear. Leave it in Drive, and the transmission is smart enough to know when it needs to shift. Leaving it in 1st gear is taking a chance of overrevving the motor.

Actually I drive in 4-lo with the tranny in 1st quite often on the trail. The engine braking just isn't there otherwise. You would have to be pretty stupid to over-rev the engine, the audible clues are too hard to miss...

Brent

Leave it in 4Hi in the mud. 4Lo works against your tires self cleaning, especially in reverse.

If you get stuck in 4-high you can always shift to 4-lo. If you get stuck in 4-lo to begin with, you'll probably be winching!

Hunter

Unless I'm bajaing down a wash or something I always leave it in Lo. I have a manual and just use my gears. I don't go to fast and I don't have to shift the t-case. Works fine.

When the money fairy brings me some cash I'll get the gears. My last junk was an old Chevy and man it would crawl. I miss that.

I try to avoid 5th gear in 4lo.