A standard 6R140 won’t last very long at that power level, I am not sure who else needs to know this. I recently paid $7,000 to rebuild mine, so I can say that with confidence. I will be pleased to respond to any inquiries you may have.
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You could have saved yourself $7,000 by doing some research or talking to people with real-world experience. What made you think a transmission designed for stock power would hold up when adding an extra 50% without the right supporting modifications?
But I will take the bait: Who wrote the files? What year and model is it? How many miles does it have?
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Some of us learn from others’ mistakes, while some of us need to experience the hard way. To be fair, there are plenty of diesel industry experts doing podcasts who rave about how much power this transmission can handle in stock form. They just never mention the longevity aspect. 
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How many of those miles were spent at the 200 hp level? Did you take the truck to multiple shops for different opinions?
Can I play devil’s advocate? Your post history indicates you have had a few mechanical issues with this truck before, including turbo problems and a transmission issue around 60,000 miles. It seems like the 200 hp setup held up reasonably well, all things considered.
Do you monitor live data at all?
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I always keep an eye on things through the EZ Lynk app whenever I drive it. Most of the issues I have mentioned have mysteriously resolved themselves, except for the valve body problem! I would say it held up pretty well, especially since it was on that tune for nearly 80,000 miles.
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It definitely has a lot to do with driving technique. 80,000 miles is not too far. During that period, did you perform any transmission services? Were you hauling anything or were you out on the street racing every car?
Many trucks pass through trannys while in stock. HP is most likely more affected by improper maintenance than by miles.
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I performed the fluids every 45k, no. I did not race every automobile, but I did occasionally give it my all. towed something about every month.
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Yeah, operating at the 1,400 ft/lbs of torque it’s rated for will do that.
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I don’t know about all that but yea lesson learned.