I just finished the GAP and PA Bike Route S from Bedford to Philly with a few modifications of my own. With those modifications, S is fine until you get close to Lancaster. Don't expect much nice riding between there and York.

OP: Send me a PM if you want more info. Route S uses a lot of PA 23 when it's not necessary. I know some nicer, quieter roads, especially if you want to camp at French Creek State Park, which is nice.