The first month of my daughter's life she went on a 10-hr car ride and 5 six hour car rides. She is soooo not a car baby either. Refuses to sleep much at all. On the 10-hr ride, I managed to go about 2-3 hours before actually stopping. I judged when to stop by when she cried non stop for 20 minutes. In any 3 hour period, she would cry for 10-15 minutes, stop for 10-ish minutes, cry for 10 minutes, etc. Only when she went 20 non-stop did I stop. I also figured she was hungry because she was eating every 2-3 hours at that point. On the 6 hour car rides I managed to stop only once in the middle to nurse. One thing that helped tremendously (I unfortunately didn't figure it out until our last trip) was how to swaddle her in her car seat. I also found a particular CD of music she likes and if I swaddle her and play the music really loud, I can usually get hour long stretches without crying. Good luck!!