Those numbers are close. I've done it twice. There are numerous ups and downs between Crescent and Bearpaw. You lose 1.5k alone, to be regained, dropping from Bearpaw to Lone Pine Creek.
I just revisited my
mileage table (made by going over a topo with string and a ruler), it is 6.4k gain, 2.5k loss, and 20.67 miles from CM to the Gap.