We are planning almost the same trip in the reverse order, next May, but from Florida. Version A was for 3 weeks, Ver B is 4 weeks, but need to figure out how to get that much time off. Her job can do it but mine is the challenge.
Several years ago we did an 18 days trip from Florida to Petrified NP, Flagstaff as our base (no RV). had to take a day off just from the travel once we got there. A day at Grand Canyon South Rim, day at Sedona, another couple of days for some of the sites around Flagstaff. Then we decided to head to Vegas for a base, do a day in Death Valley, another night in Vegas, then do Zion on the way back to Flagstaff (crazy). By the time we got to Vegas, we were wiped out and cancelled Death Valley. Spent 3 hours in Zion (wanted 3 days after I got there). Kids and wife got sick so we had to slow donw. 6000 miles in 18 days. Did the last 1100 miles in one shot. It was too much for us and I was the oldest at 36.
Now with RV I can do 600 miles in one day, but not in consecutive days. Most road trips start out around 7 pm, drive 4-5 hours and hit a Walmart for some sleep. It's a nice way to chew off some miles with less traffic.