If you have a 30-40 pound body on your hands and other evidence, but y0u don't have a vehicle, you really don't have a lot of options. It's not like he could call Uber or Lyft, or take a suitcase on a bus, or even mail a 30 # package from UPS.
I really think he had to discard her body very close to the scene of the crime and any other evidence after that. I think they need to re-think this and go back over that 1mile radius - OK make it 2 or 3 miles. I just don't think he had a way to take her to Hyrum.
Did I see something way upstream in the posts that he was observed without his backpack? That would at least pin the farthest possible disposal site, for me