Just passed 305,000 miles yesterday, shift kit from Transgo, always anal on maintenance and using name brand filters and fluid-usually always use valvoline. The biggest thing that helps the most is keeping your head out of your butt and not flooring it with a big chip empty or loaded. Have a Van Aaken Smartbox R on mine, use middle setting when I tow. Everyone claims the 47RE is a weak transmission, I think it suffers from guys bein stupid with their pickups more than any flaws of its own personally just wondering how many have auto trans with no issues....and what you did to make them that way.
WORD! Too High Temperature is the "typical" death of automatics. A precise built "for your application" and "typical/intended" use & level of HP/TQ + good maintenance = fluid, filter, band check/adjustment, correct line pressure and keeping the temperatures in-check should provide long life. My DDT built eons ago has over 125k miles and still goes strong. There have been a few issues over the years which are typical - 2nd gear start, hunting for OD all of which would occur whether or not the trans was stock or built were easily remedied with new "wear item" parts Solenoid/Transducer and noise filter.A "properly built" transmission is very strong and very reliable. Expense billet shafts and drums do little for strength until your in the high hp/torque numbers. A good billet low-stall torque converter, better line pressure, and more clutches is the key to keeping transmission temps down. If you're in stop-and-go traffic, put it in neutral when at light to cool it down.. If you want your transmission to last, keep the temperature down. That's it.