One problem related to transmission failure has been reported for the 2013 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2013 Ford Mustang based on all problems reported for the 2013 Mustang.
I purchased a used 2013 Ford Mustang boss 302. The car only has 9,000 miles on it. It only comes with the 6 speed manual transmission. It has a clunky shift between 1st and 2nd gear and 5th gear. You must shift very slowly when it is cold or it will grind the gears. I have looked at several Ford boss302 facebook groups and everyone states they will have clutch lockout if they shift at high rpm's and ultimately will have transmission failure due to a clutch that is unable to provide enough clamping power to to hold the flywheel when shifting. Numerous users stated that as soon as they upgraded to clutches by mccleod, exedy, or mantic, the problems immediately went away. They all state it is not the transmission, but the faulty clutch that causes the transmission to fail eventually. The boss 302 engine has a 7,500 rpm redline which is higher than the other coyote 5. 0 liter engines. The clutch can not handle this high rpm limit. So, basically Ford sold a performance car that you can't drive anywhere near its limits because of the faulty clutch/transmission. They should be required to replace the stock clutch with a higher quality aftermarket clutch. If they replace it with the same Ford clutch, the problem will repeat.