This should be pretty much flat after Tahoe right?
Depends on you define 'pretty much'. Tonopah is at 6000 feet elevation about the same as Tahoe. Nevada is a basin and range state with lots of north-south mountain ranges. None of the hills will be as long as US 50 from Placerville to Tahoe but it is not flat like Sacramento or Kansas.
Fill up when your fuel gauge says half. Don't leave Tonopah without a full tank. Be careful if you travel at night as there is a lot of free range for cattle. Black cow, black night standing on a black highway kind of thing.