My old man's '01 Ford SD just past the 620,000 mile mark,same auto ****** and engine.He has the fluid flushed and filters changed about every 30,000 miles and he tows his 30' horse trailer or the 40' flat bed trailer with on average about 20,000lbs of weight all the time(10 or more times a week).The trans is totally stock,the 7.3 PS has a 180 BullyDog chip and 5" straight pipe exhuast.
Check out most of the drag race cars and you will see automatic transmissions also since they can be built stronger and they break less parts when luanching,gotta love that trans brake
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