What is the max miles for the transmission warranty to stay in effect?

Not exactly sure on this particular vehicle but 50,000 miles is a fairly standard warranty distance of coverage for a lot of vehicles. Most transmissions should last anywhere from 100-150,000 miles depending on model and make and the amount of abuse they're put through. Sounds like you might be lucky by about 10,000 miles for that warranty. I would check it out. Best of luck.