At what mileage should I have my transmission fluid flushed

25-30,000.

I would not flush the trans but change the fluid and filter every 50,000 miles or less. In my opinion flushing is a marketing scheme to extract lots of money out of people for little to no benefit.

I grew up with my tranny guy. After one failure on 1996 he told me to throw the 90K Ford recommendation into the garbage and bring him my vehicles every 40K miles for a filter change and fluid change. Took his suggestion and my 96, 99, 2003, and 2007 explorers are still going strong with almost 700K miles on all combined.

At what mileage should I have my transmission fluid flushed for my 2013 Ford Explorer ?

I always change the fluid in my cars and trucks at 40K miles. If you have a 6 speed tranny in your ford (6R60 or 6R80) I have it flushed after every other fluid change.