Thank you very much to all of the people who replied to me so quickly,
but it looks like I've got the problem licked.  I went out and looked at the
battery connections like Stephen suggested, and, sure enough, the battery
connections were loose on both sides.  I guess the vibration just loosened
them over time.  I dabbed some dielectric grease on the terminals, snugged
the bolts back up, and everything looks good.  If I experience any further
problems, I'll be asking for more help, but the connections were pretty
sloppy, so I suspect that's the root of it.
Thanks again!
-Jason Stevenson

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