How do you repair a sludged 6.4 turbo diesel

I would use one of the full-synthetic HDDOs in the link below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1415281

Change it every 3,000 miles, until it improves. The natural higher detergency of synthetics should safely clean the engine.

This link may also help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-12.html#post2162069

Auto-RX is another product that is highly recommended for sludged gasoline and diesel engines and transmissions. Only use Auto-RX with conventional diesel engine oil. You can check it out and buy it online.