Ok, this is a NON Mopar specific question, but I know I'll get an answer here - as my attempts at a brand specific forum have turned up little for me.

99' Grand Prix, 3100 engine. Car will only start when jumped. I have:

New battery (800 crank amps, Duralast)

alternator checked; charging just fine

starter taken off and checked; fine

checked for voltage at the solenoid on the starter when key is turned, checks out fine

took ground cable off, clean connector up

new neutral safety switch too

WHAT is wrong with this car??? Starter bad even though it worked on the test bench? I am just about ready to take it to the mechanic, which is a low in my book.

Thanks for any help.