Did you get it sorted out? if not i would suggest that if possible just leave it with the shop and let them the mechanic drive it home and see if it happens to him. I had roughly the same issue with a different car but turned out to be an isolator in the distributor that was the problem (would heat up and shut the car down let it cool off and would start right up). also you don't mention if it turns over when you try to start it. like i said if you can let the mechanic drive it home and back and see what happens could be something really simple
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2008 Ford Escape AWD 250,000kms
going to need my head examined buying a car with this many miles on it