jackrae:
Suggest you get yourself a hall sensor with a 5 volt output range. Total isolation between measurement and output so you can stick into any part of the circuit. Yes they cost more than shunts but resolve all the problems associated with shunts.
I am not familiar with a Hall effect sensor that measures current. Can you suggest a part or a link to further reading. I do like the thought of isolation from such a high current.
RWW