Well there's no way of eliminating the hills through mountain country, obviously.
In general, if you want to minimize the grades, stick to the Interstates. In this case it is I-80 all the way. The standard maximum grade on them is 6%. Alternate routes to get you to the same place would likely not have the same maximum.
That road is full of RV's, and likely a lot of them are worse off than yours. Just take it easy, accept the slow speeds on the climbs, and use that same slow speed for the descent. You'll be just fine. Relax, enjoy the views, and try not to think about how much fuel you are using -- there's plenty of gas stations!