I looked at a few of the crash dumps submitted from your IP address, and they were all different, seemingly in random places, and there were also some signal 11 errors.
If it has DIMMs you can pull you might try swapping them out to make sure it isn't a RAM problem.
The way it's acting is, in general, indicative of a hardware issue. Aside from RAM, it could equally be a power supply issue, cooling, the MB/BIOS, the HDD, some combination of the above, or a general issue with that hardware and FreeBSD.