Here's what I've come up with, as a generalization, yet an accurate one. For the most part, grades west of the Mississippi, especially on interstates and good 4-lane federal or state highways, are LONG, but not especially STEEP. They have more room out there to build highways on. In the east, especially along the Appalachians in NC, Tenn, Georgia, and in the Adirondacks and such in New England, some of the grades are, interstates not included, STEEP, but short. There are some grades in West Virginia up near Morgantown that are 7% on an interstate, but they're only a half mile or so long.
So the west has long, shallower grades, and the east has short, steep ones. It's all about how much room there is to build roads. The east is all folded up and narrow, compared to the west. Steeper grades, tighter corners. Hell, there are some bridge off-ramps in the east that are steeper, shorter, and scarier than anything I ever drove out west.
Generally.