Awf Hand from Chippewa Falls, WI on 10/21/2016 2:33:10 PM:
The GAP may require a bit more planning simply because there isn't a hiker/biker campsite every few miles. My daughter (9yr old) and I did the same first two stops you did, but found we averaged over 21mph (yeah, I know... speed limit 15) from the divide to Cumberland. With this extra "boost" we pushed on and camped at Lock 75.
I think you'll find the second half of day 3 just flies by.
We met a fellow along the trail who told us to be sure we visited the museum in the basement of the WM Railway depot. WELL worth it, and it was a good break for us as the temps were in the mid-90's. -Highly recommend.