99 F250 cc bone stock with 308,877 miles. Tranny rebuilt twice. One @ 217,000 and the 2nd one @ 296,000. Worked hard and towed many a goosenecks. Have replaced usual: water pump,belts and other regular wear items. No secret to the maintenance, just regular oil/fuel filter changes and drive the hell out of it.
99 f250 cc 308,000 miles and counting.