There's been lots of debate over brake fluid changes. The OEMs currently do not advise doing brake system flushes, but the aftermarket disagrees. As far as that goes, we test the fluid for copper content, then suggest wheather or not to change it from there. We usually suggest it at around 200-300 ppm copper content.
However, with the older trucks having vented master cylinders, more frequent flushing is a good idea, as the fliud will ablsorb moisture.
