They had issues with cracked heads in the earlier years due to a casting problem.
I am not well versed in specific areas of 'QUOTE' problems. As such I offered my two bits worth of user results.
I offer a few comments based on my experience with a '85 6.9 as well as the '88 7.3 motor. Combined mileage for the two is over 300,000 miles. I towed my 40' 3 axle Chaparral goose neck trailer loaded with race car, spare motor, parts, tools, nitromethane and alcohol with a combined gross vehicle weight of just over 22,000 lbs all over the So Western US. Yes it was 'slow' going over the Grapevine, Cajon Pass, and even the Rockies. I always geared down and kept the RPM's at 2800 to 3000. Yes I blew black smoke at times.
I did not add any HP increasing tricks like turbo, propane, water, nitrous, play with injection timing, after market air filters, exhaust, or whatever. What I did do was remove the big stock muffler, cut open the top, gutted it, and put a straight pipe though it. It looked stock unless you actually felt up on top of it for the welding. I did not have any motor problems in transit to and from with the heavy truck-trailer combo.
That is not to say that there were/are some bad castings that appeared at random. So like saying: "you could catch a cold if you go out of the house", chances are prob pretty slim as the miscast have prob already joined the myriad of Chev's in the scrap yard.
Finally I am off my soap box and off to McDee's for some of their fifty cent 'senior' priced coffee. So like the lady,?, sez; you spends your money and you makes your choice, I'd go for it, you????