Most people pulling RV's use I80 to cross the Sierra that far north. US 50 is a good choice getting to Lake Tahoe from the Nevada side in an RV but not a good choice going west further into the Central Valley while pulling an RV. I-80 will land you on state route 49 in Auburn and from there you can choose any number of different directions. California is a very large state to see everything in one trip. The approaches to Yosemite are very steep from either direction and best done as a day trip (such as from Sonora). Highways 99 and I-5 are the two major North-South freeways.