I have no idea what things are like out there now, some of their job ads in the had been a bit misleading when it came to pay. Back in 2005, they would advertise the job as paying 63k, but that was if you worked 5 extra days of overtime, and not a 20/10 schedule. Spending 25 days a month in Kayenta or Chinle is not everyones cup of tea. Spending any time there isnt for that matter.
I would imagine that 90k they are advertising, is dependent again on giving up some of your days off to get that pay. 5 days a month off would not be enough for me, because it is going to take a just to leave, and a day to drive back.