Well that schedule I posted above involved no reservations except at Yosemite and Lassen and that was to get into a CG inside the park. Otherwise it was all drive until we felt like stopping and then calling ahead to make reservations for that night. We only were told they had no spots at that CG once in the whole trip and easily got into the next CG on the list. Having a good CG directory makes that possible we carry the 'big book' (now called the Good Sam's Travel Guide) with us for that reason. The online cg guides are OK but none has the 12500 listings that the book has.
Furthermore once you are away from DV everyplace on that schedule is somewhat cool (temp wise) and we completely avoid the CA h*ll of the central valley roads. The only city we drove thru was Sacramento on the way north to Lassen.
My advice is to AVOID I-5 (pothole city) if at all possible, I doubt that US-99 is any better. Whatever CA is spending money on, it isn't roads. Of course they are probably paying the guys who fill potholes $250,000/yr. California residents can tell you a lot more. We found northern 101 to be fine but we were only on the last 100 miles or so of that going north. The interior roads to Lassen were drivable.