I did it 3 years ago. Took me two days. First night near the Colorado river. Second night south of Neuquen, a touristic small village with a lake.
I recommend staying at quemquem campground in El Bolson. No need to pitch your tent, there is a big hut where you can sleep for the same price, and Dicky Harvey is a very entertaining manager.
There is a crossing south of Santa Rosa, take the Northmost less travelled road across some hilly area, it s just beautiful.
In El Bolson, 42 parallel south, prices of gas are 50% off.