thom, my crew cab had a similar problem about a year ago.  i was not able 
to find the real problem for the  starter not engaging, but fixed it none 
the less.   i installed a "hard start kit" from bosch.  it basically 
bypasses all the wiring in the front of the bus so that all the cranking 
power from the battary will go directly to the starter.  The theory was 
that all that old wire up to the front of the car lost some of the power 
for the starter.  Whether that is correct or not i do not know.  i do 
know that for about $15, my problem was solved.

take care and God Bless
matt