What would make overdrive go out on a 1994 Dodge Ram 2500 mins Turbo Diesel?

I have a 1994 Dodge Ram 2500 mins Turbo Diesel. It has 344,000 miles on it. It has an Automatic Transmission. I would like to know what would make overdrive go out of it. The guy who owned it before me used it to pull gooseneck trailers. Could this be a big reason for the transmission problems??