the first couple reboots were very slow, and would get stuck on "loading visualizations".

Yeah, I'd suspect the hard disks, especially since you're describing vibration problems in the car.

We just got done discussing this with someone else in another thread. The disk drives can tolerate moderate vibration at intermittent intervals because of the caching. But if you're driving along with a constant severe vibration that never stops, then you will be preventing the disks from being able to fill the cache, and perhaps even doing damage to the disks too.