Thanks, The_Bouncer for sharing your experience as well as the advice you got from Gardyloo and others on this forum.

It is a shame we had to cut out Grand and Bryce Canyon as well as Zion, but I'm convinced it was the right decision that will make our trip much more relaxed and enjoyable. Especially Grand Canyon seems to require some hiking for the best views, which would not have been feasible because of the heat.

We did keep Death Valley in the itinerary with the understanding that it will get extremely hot there. Average low at the time of our trip is 88° F, so we will be able to enjoy the sunrise in bearable conditions but will need to be out mid-morning.