You're kidding right? 59K is barely broken in...if your C is having trouble on the hills it may need some basic drivetrain maintenance. Going to a unit that is "beat up" and with coffee grinds in the transmission fluid PLUS a $300+ monthly payment just because it only has 10k miles is foolish IMO.
From what you describe, you'll likely be facing more in repairs, cleaning and maintenance on the new unit vs. the one you have. Anytime is the right time to trade, if you have the cash and find a unit you like more than the one you have....but this doesn't sound like a deal. I would pass on this and keep window shopping.