WOW! Awesome trip. Leaving DFW in August might make you The Burning Man. Just kidding. August is the month that I try to be somewhere high in the Rockies.
Now, as for daily average mileage...
In a previous lifetime I flew to Salt Lake City. SLC was in a heat wave, 105+ during the day. I rode out of the airport about 10pm & stopped about 8am the next morning in Logan, UT. 70 odd miles as I recall. For the next 12 days I rode anywhere from 35 miles to 75 miles. The first week heading to the Tetons & Yellowstone and climbing over passes all the time nearly killed me. By the time I got to Yellowstone I crossed the Continental Divide 3 times, the first time in the afternoon & twice the next morning. Piece of cake. My only mileage goal was the 750-760 miles I needed to ride to get back to the airport. In between I stopped where it was convenient for me at the time. Example: Afton, WY to a forest service campground on the Snake River, 35 miles. I picked that spot because I did not think that I could get to a campground in G.T.N.P. before dark and knew that Jackson, WY would be expensive. Quite by accident, a group of Boy Scouts and adult leaders camped next to me. They invited me to join them for a raft trip down the Snake. Afterwards they made me eat elk steaks cooked over an open fire. A day I'll never forget. I made up the miles from my short day later in the trip on flat to slightly downhill grades in Idaho and arrived back in SLC the afternoon before my flight.
ps: OOPS! I got this thread confused with your other thread about daily averages. My C.R.S. must be acting up.