I've got Duramax diesels. The only one to watch out for was the 2001-2004 LB7 engine code Duramax. They have injector issues to the tune of $5k+ every 75k-100k miles. The 06 and 07 LBZ engine code Duramaxes were the best of the pre-DPF emission models. I bought an LBZ new and still drive it almost daily. Mine's tuned, has 1 Ton DRW double spring packs and frame perches, solid front and rear sway bars, etc... It's set up to work— to tow heavy and haul ass. The LMM and LML engines are also very reliable. In 2017 they've upgraded to the L5P. It's my understanding that the L5P is being produced by GM rather than Isuzu. I've also got a 2016 LML. The interiors on the new GM trucks is fantastic. There's tons of integrated storage. The GM diesel equipped trucks ride better than their Dodge and Ford counterparts. I've previously had a Cummins equipped Dodge. I haven't owned any Powerstroke equipped Fords, but have been around plent. They're very popular. I find the Fords sit unnecessarily high and I don't want to climb in and out of one all day. It's also been my experience that the Fords ride like buck boards. If I was looking for a 450 or 550 class truck, Ford would likely get the nod, but at that point there's better value in a 33K GVW single screw with air brakes. That's another topic.
I haven't kept up with all the Powerstroke iterations. The 7.3L is legendary. At least one later version, IIRC the 6.0L, had issues with head studs stretching. A problem for which there are well known and proven fixes. Someone more familiar should speak to the Fords. I loved the Cummins, but the Dodge wrapped around it was a POS. In under 2 years and 39k miles, the front end was shot.
Good luck in your quest. Anymore, they all make a pretty good truck.
