I have had just about every GM Diesel starting with the 6.5, through the latest designs (Isuzu and Opal based). The 8 Cylinder engines were an Isuzu design. The only one I have had issues with was an LB7 (2003 MY), injectors. I had an LBZ (2007 MY) that I gave to my son, it now has 375k on the clock, 1 glow plug, that's it, and he just left with his kids and 5th wheel in tow for a 4,500 mile round trip vacation on it. I drive a 2023 LP5, it too is has been trouble free, but only has 20k on the clock. I am hoping it will go as far as the LBZ did, only time will tell. I am not an LML fan, they either ran without issues, or they were plaugued with emissions and fuel issues, not sure why.
Now for the Opal design, LM2, LZ0. My Company has probably close to 100 or more of them dating back to 2019. The highest mileage LM2 we had, hit 174k before it was taken out of service and sold. It was sold due to mileage, it should have been sold at 125k, but vehicle shortages prevented us from taking it out of service sooner. The only issues we have seen, and it's only been a handful, a few DEF Gauge Reading issues, one turbo, but that's about it. In the 2019's there was an issue called no start, but that was when they first came out, I think it was a sensor, but that was back a few years. Some have complained about excessive oil consumption up to about the 2021 MY, we never had one, and still don't have any with that issue. I have around a dozen or so parts runners, they basically pick up parts and take them out to job sites as needed, they rack up the miles, mostly due to the geographic area. We build large valve systems, flood gates, and steel turbines. The parts are not the type where you can drive to HD or Lowe's and pick them up in the plumbing section. These folks drive around 40k-50k a year.
Diesel or gas, if you don't maintain it, expect to pay for it down the road.
