That sucks! Especially this close to the holidays. You're lucky it didn't crap out while you were in the mountains.

Do you trust that mechanic? If not, get a second opinion. How does the motor simply low up while you're warming it up? Wouldn't there be some indication things were going bad?

I second blacklabel's suggestion- find a junkyard or second-hand motor to put into it. There's a zillion JGCs in this state.