I've owned 2 Ford trucks with the 6.7 diesel engine. The first was an early build 2011 and now a 2013. The 2011 did give me a few issues that the dealer took care of. Every year they make improvements to the engine.
My 2013 has 45,000 km's now. It has been trouble free. I have used a fuel additive since new. You may read about fuel related problems. I get great mileage. The power is incredible. I don't think you'll be disappointed. With that mileage you will still have warranty. If the price is right I wouldn't hesitate.