Discription of Events: Driving through Rockford, WA, we had a truck that was continuously swerving into the opposite lane and into the shoulder. Almost hit a few people in the opposite lane and nearly fell into a ditch. Was also doing 45 in a 60 zone. We reached Idaho, near the city of Worley, when he suddenly slammed on the brakes on the highway in front of us. He seemed to be drunk. Had, what we believe to be, a Chevrolet Avalanche that was black, possibly a dark blue. It was very dark out.