We live in the Monterey area and our favorite and only route is to go south on Hwy 101 to the Paso Robles area (some of the best wine tasting in the state without the crowds in Napa & Sonoma or the wine snobbery). We then go east on Hwy 58 to Barstow. Great place to stay in Tehachapi is the small RV park beside the glider airport at the east end of the town.
From Barstow you can then head south on Hwy 15 all the way to San Diego. You miss 95% of the LA basin and its traffic.
I-5 is the slowest highway in the state as it is two lanes in each direction and has most of the heavy trucking traffic as the truckers avoid Hwy 101 to save fuel. As a result the right lane is occupied with the truckers and then motorist speed up and pass traffic using the right lane and then dive back into the number one lane and the other drivers have to hit their brakes. Having this happen time after time and mile after mile is tiring and nerve racking and you are going through the ugliest part of the state.
