When planning a trip, I used to use Flattestroute.com to see how steep the grades were, but that site has been taken down. Is there a comparable site?

Sorry can't help, as although we have mountains on 3 sides and water on the other, it isn't something we worry about. Even with the old SRW F-350 we never had any issues handling the grades throughout the Rockies.

Good luck finding something.

I can understand not wanting to tow up Pikes Peak or similar, but why only flatlands? You have a weak truck? If it's a diesel, which is almost a must for our RWs, the newer ones are very adequate/capable towing up plus with tow/haul & exhaust brakes are more than adequate coming down.