Sounds like a beautiful ride!

On the elevation thing - I have found Ride With GPS to be wildly inconsistent and inaccurate in gauging elevation gain. I looked on Strava, where cyclists record rides using their GPS (much more accurate), but could not find anyone having listed the ride, or anything in that vicinity. But my conclusion would be that RWGPS is high. (I pre-rode the middle section of a 1000k I am working on for my club and got 10,000 feet with my GPS where RWGPS was saying 19,000 feet.)

On the numbness thing - do get the fit checked out. I fractured my scapula several years ago and that hand is much more likely to stay numb after long rides. I think there may be some underlying nerve damage or frailty in there because of the fracture, so that may be an issue for you. But fit (and body position on the bike) is your first line of defense.

And if you can do 75 you absolutely unquestioningly can do 110.