Need gear advice 98 Yukon

Hi, just bought a 98 Yukon. I live in a rural area and I have to drive up a steep mountain pass, should I be putting the truck in 3rd gear? Or do I keep it in overdrive at all times?
Thanks for any replies

It will down shift as needed and depending on speed and throttle position. No need unless you are going up a really steep grade like in an off-road trail or something. atriot:

Thanks so much:giggling: