Death Valley in June is just foolish, no good reason to be there with alternate routes available... and they won't be all that cool.
You will need to be able to monitor you trans fluid as well as well as engine coolant temps. Don't think you can safely rely on the dash gauges. A Scan Gauge will give you all the info you need. Keep the F-150 in Tow Haul to help keep the trans temp down and for better control both going up and down{it will cool your brakes big time}, those very long steep grades.
We did it last year in September and the forecast high of 88 turned into 110 by the time we got to Furnace creek. I was running our V-10 Class C and pulling my motorcycle {bike and trailer are 1,000#}, and it was not fun. Saw 230 degrees of trans fluid and 224 of engine coolant but they both dropped like stone {as they should}, once we cleared the summits.
As always.... Opinions and YMMV.
:C