Personally I don't like the Cajon Pass (I-15) and I prefer the Grapevine (I-5)
I would come up from San Diego on the 5 and then connect up with the 210 to bypass the heaviest of LA traffic (This is still a major byway and if you hit it at rush hour you could find yourself speeding along at 5mph) If your traveling on Sunday, or mid-day (before 3:30) on a weekday you might do just as well just traveling all the way north on the I-5. The Grapevine has a steep initial climb, which I could easily handle in my Adventurer towing a Saturn and now in my Allegro RED. After the first 6 mile climb the road becomes less of a challenge until the downhill grade. This is a steep constant drop, but if you maintain your speed you should not have a problem. The Allegro diesel went down the grade at 45mph using only the engine brake, I never hit the brakes. My Adventurer (gas), I would hold my speed to about 50mph and tap the brakes every time it accelerated past that, bringing my speed back to 40 and letting it creep up. I sounds scary, but really, keep your speed down, and it is not a bad drive. The reason for trying to bypass LA traffic is the total number of cars and truck on the road. Drivers are in a rush to get home, they don't let you change lanes, they pull in front of you, like you can stop on a dime. Just stupid drivers. Avoid rush hour. If you get caught up in heavy traffic, pull of the freeway, stop and have lunch or dinner, and try again in a couple of hours.
Enjoy your trip.
