we had a 7.3 that was upgraded with a turbo and a few parts. It is well over 300k now and no issues other than normal wear and tear items.

we also had a 6.0 for two years. put just shy of 190k on it. initially it ran like crap but the re-flash from the dealership it ran awesome.

Both used for hauling a two car trailer.

Only drove a new 6.4 once. Seemed to have more power all around and a nicer ride, but the price tag was too scary lol.