My wife and I took a trip to Disneyland this past September (her 1st trip to Cali, my second). 6 days will give you more than enough time to ride practically everything. We had 3 days...1 full DL, 1 full DCA and then a split day between the two. The only rides we didn't get to ride were Peter Pans Flight (but we've ridden this dozens of times in WDW...so no big deal), Haunted Mansion and Space Mountain (both were closed for seasonal updates - ie. Halloween). We fairly easily fit everything else in....granted we went in September though so the crowds were a little lower than probably August will be.
It seems California Adventure had a bit less to offer than Disneyland, but Cars Land was probably one of the coolest themed areas I've ever experienced at any Disney park. It's literally like walking into the movie....we rode each ride in that area 3 times...with Radiator Springs Racers being one of the greatest rides I've ridden, it's so much funner and better than Test Track.
As for Sequoia, it was also one of our stops. You luckily get 2 days and we only had 1, but that also involved travel to and from Hollywood. It's a fantastic park and though my wife wasn't sure about driving 3-3.5 hours to see it, it was something we both had agreed would be a good change of pace. If you get the chance, climb up Moro Rock to the top. It has spectacular views of the valley below to one side and the mountains off to the other. It's a fairly simple climb to the top since there are steps all the way. In some areas the steps are narrow, but wide enough for a single person to pass at a time. Just keep in mind that people are also coming down and as long as you aren't in a rush to the top things go pretty smoothly. My wife was very concerned about the climb up, but it was easier than either of us had read about. The road leading from the entrance (near Three Rivers, CA) to the top where Moro Rock is, was under construction while we were there. It seems that it may be complete, I couldn't find any info, but if it's not they have a stop light which if I remember correctly is on a 20-30 minute timer. Make sure to fuel up the vehicle before entering the park as there are no gas stations once inside. We got caught at the light, but only waited around 10 minutes. People generally got out of their car to stretch and take pictures. Kings Canyon NP is linked to Sequoia as well, so if you have the time you may wanna head up that way to check it out as well.
