As a test, I made a route using Strava Route Builder, just clicking along the most popular bike roads somewhat near the GAP trail. The route. It has some pretty steep climbs at mile 50, mile 60, and mile 160.

See the "segments" list on the route for the climbs. For example, this 1000 foot, 7% average grade climb.

To make a route (you probably need a free strava login), click the map options and turn on the Heat Map, and click the Elevation On option at the bottom. Then you can click along your route, and undo or drag the route line to a different road to try alternate routes. Some of these roads could be gravel or bike trails.

There's a "Minimize Elevation" button that might help. It often takes a much longer, flatter route. But you still need to cross the mountains.

Strava will use the most popular roads instead of the most direct route between two points. The final route can have a lot of turns, probably best used with a GPS device.


~~~~

Here's the Strava Heat Map for southern PA. Click the Toggle Labels button to show town and road names. There's a lot more riders near cities, so those have more dark red roads. I avoid light blue roads if there's a nearby dark blue or red road -- riders are avoiding the light blue roads there.

The URL changes as you pan and zoom, so you can bookmark that view.