GPS works throughout. Sure there could be a spot where you briefly lose signal due to interference.

There aren't many rounds at all you need to worry bout for your trip.

I-15.

UT9 from st George through Zion to Kanab
US 89 from Kanab north to UT 20 turn off ( turning lane here for left turn)
UT 20 and UT 14 cross roads between US 89 and I-15
US89A Kanab to jacob lake
AZ 67 from Jacob lake to north rim.
UT 12 from US89 to Bryce.

Roads are well defined and signage is very good.

You should make it by 2000... The only issue is this is rush hour traffic at 1600-1800 so heavier traffic n Vegas.


Some of the black spots would be going through the Zion tunnels. Elsewhere you will be fine.

You could print a map frm online that would be sufficient.