Anet
I would consider an overnighter well before Stockton and options are limited taking 5 north. I have travelled from S.D. to S.F. on numerous occasions and have always been happy to take a break on the north side of Grapevine. I usually take 99 north (Vs 5) there a lot more campgrounds to chose from en route. I have stayed at a newer one in Bakersfield, close to the freeway which was very clean and reasonably priced (under $40) with a nice restaurant on site. It's directly across from Stiers RV.
On cutting over to 101, consider 152 (either from the 99 or 5) with an stop at Casa de Fruta Travel Park (408) 842 9316 on the Gilroy side of Pacheco Pass and east of The San Luis Rey Reservoir . However, that puts you on 101 south of the Bay area and SF traffic, IMO, is not good at the best of times. I think I would take I-80 east from 5 at Sacramento, then 12 (north) toward Flag City, or Choice #3 as Tom suggested.
If you do take 5 north , there is the Lost Hills KOA at 5 and SR 46 (661) 797 2719 or the San Luis Rey RV Resort, 3 miles west of I-5 at SR 152 at Los Banos/Santa Nella (Pea Soup Anderson's) (209) 826 5542, I haven't stayed at either so I can make any recommendations other than their convenience and proximity.
BT