Starter Woes

["Mike Stenstrom" <stenstm@domain.elided>]

Reapers,
   I've been having a problem with my '74/345.  For the last couple of weeks
it will start 3 - 5 times and then just die.  I can tell when it's not going
to start any more by the sound it makes on the final start - kind of a rod
knocking sound - the next time the key is turned there's just no joy in
mudville.
   This morning there was not even a click.  Threw a jumper cable from my
wife's car and at least got some turning.  Did not stick around long enough
to finish the jump.  This really sounds like a battery problem and the
battery IS more than four years old.  I'm taking it to the parts store to
test it under load tonight after work.  I think it will fail.  My question
is (if the battery is NOT the problem): What and how can I check to isolate
the problem?  None of these start failures are when the engine is hot.  The
battery meters at 13.2 volts, but drops to just 2 or 3 volts when I try to
start, turn on the lights, or even the radio at low volume.  I'm really
stuck here - and using my wife's car as a jump start vehicle cost me a LOT
of cool truck points!  Thanks in advance for the help,

Mike Stenstrom