I just rebuilt my kernel with the options below disabled, and I no
longer get the silo overflows, dropped packets, VJ errors, etc.  I'm
going to rebuild my kernel with one of these options enabled at a
time, and will report on which one(s) seem to be causing my COM
problems.  

#options              "M68020"        # support for 020/851
#options      PPP_BSDCOMP,PPP_DEFLATE # BSD compression for PPP
#pseudo-device        tun     1               # network tunnel line discipline
#pseudo-device        bpfilter        4       # berkeley packet filters