I did my first drain like you at 20k. It was nearly black. Ever since I have used Mobil 1 and it has been red everytime. I don't think the factory fluid (motorcraft I'd imagine) is very good, espcially with the heat given by these transmissions. The mobil can take extreme heat much better, and assume you keep a close eye on it should give your transmission plenty of extra life. I feel sorry for the people who got 50-60k on this car with the original fluid still swimming in there.