4 wheel drive on 1996 Isuzu Trooper

How do I get my trooper in 4 wheel drive when traveling on a highway in snowy conditions?

Asked by for the 1996 Isuzu Trooper
The manual specifies that the Shift on the fly option can safely transition to 4 Hi only at up to 60 MPH.
4 Lo transfer requires dead stop and neutral or else you get a grind. I have found over time the vacuum operated
locking hubs tend to get sluggish in cold weather.