Don't know of any BUT the Durango is shift on the fly.
Basically you can go between 2H/4H at any speed, 4L is a different
story, For that you need to stop, put the trans in neutral, then put it
in 4L, then shift into drive or reverse. The limit with 4L is about 15
MPH.
As for when to use ANY 4 wheel is easy. When the surface has some slip
you can use it. DO NOT USE 4H/4L ON BARE PAVEMENT, OR ON ANY OTHER HIGH
TRACTION SURFACE. It does bad things to the transfer case and front and
rear differentials if you do.

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Steve
> Is there a website I download owner's manual for 99 Durango? Specifically
> I'm interested how to shift into 4H/2H - can it be done while moving?
>
> Peter
Peter, You can order a new owner's manual from your local Dodge
dealer. Usually, you can shift from 2H to 4H while driving up to 55
MPH.