We make this drive every summer on US 95. Many sections are two lane only. There are three big grades traveling north, Horseshoe Bend outside of Boise, White Bird Hill between Whitebird and Grangeville and Lewiston Hill, which climbs from Lewiston to the Palouse. We pulled a loaded tent trailer with a Ford Windstar on these grades (I know...we were probably a bit underpowered) and we did fine. Parts of the the two lane sections can be narrow and twisting, we take it easy and use the pull-outs to let people pass us. It is beautiful country and you won't regret traveling through it.