Just to throw this out there, and it may be too late for the OP, but just avoid I-5 altogether. If you are heading to any point north (except the central coast,) stick to Highway 99. The road is so MUCH better, 3 lanes both directions most of the way, and its only takes about 15-20 minutes longer. But trust me the road is so much smoother and with the 3 lanes, you won't get stuck behind any trucks for miles on end, you won't even notice the extra time!
I-5 has become horribly rutted, pot-holed, and neglected by Caltrans. While 99 has almost completed its expansion and the state is seeking to have named an interstate. So its no longer the forgotten, red-headed, step child to I-5.
But, don't tell anyone! I don't want my secret to get out and ruin my great, less-traffic, smooth alternative! One more thing , there is supposed to be (near Fresno I think) two trees right next to each other, one redwood to the north and a palm tree to the south. This is the exact geographic point between Northern and Southern California! Although I haven't seen it personally.