if you enjoyed European Truck Simulator, you'll gonna like this. California and Nevada already supplied, Arizona coming.
I'd love to drive thru Monument Valley!
http://store.steampowered.com/app/270880/
I don't know if it comes with development tools and documentation. There is a lively mod scene, but it provides mostly custom paint jobs.
Farming Simulator comes with full tools and docs, and has an enormous collection of tractors, maps and implements because of this. I have seen ETS trucks being imported in FS.
Now we only need Russian/African/South American Truck Simulator where you have to drive your truck over unpaved roads, through deep mud, over truck wide mountain ledges, escaping highwaymen and robbers, corrupt police officers, etc.
Spin Tires, that kept Oovee Studios from releasing their promised U25B, is a drive through wilderness simulator/game using big Soviet style army trucks. Only intercontinental ballistic rocket carriers are failing, and these are huge trucks!

https://en.wikipedia.org/wiki/RT-2PM2_Topol-M
Or more peaceful, Australian Truck Simulator with those "road trains", red dust, endless horizons and kangaroo's hopping in the wilderness next the road.

http://www.outback-australia-travel-secrets.com/australian-road-trains.html
http://www.roadtrains.com.au