Go to LEIGH CREEK for fuel. meet Rosie... lovely lady, and will look after you both now, and in years to come, when you next pass thru there.
From Oodnadatta - leigh creek, try to find "the marree man". best height about 3-5000'.
and as said before... try NOT to use the GPS unless you are really stuck. My advice would be to have it ON, and running properly, but covered up so that you cannot see it, but easy to get info from if desperately required.
oh... and take LOTS and LOTS of water.