5.7L and 6.2L Diesels were....not good. Sure, they would run, but they barely had enough power to move themselves.
Wanna know what kills almost 100% of ALL automatic transmissions?
Heat and time.
Heat breaks down the additives in the fluid that keep seals pliable. Heat also hardens seals. You can mitigate this somewhat by keeping the fluid changed, but you're only buying time. Once the seals get hard, they start to physically wear, and then they start to leak and the apply pistons and servos cannot hold the frictions tightly any more. It only takes a few seconds of a good slip under power to roast a clutch pack or band and lose that gear.
Some additive products contain seal "conditioners" which are nothing more than petroleum distillate swellers. Adding these eventually turns seals to mush and the clutches/bands slip and roast.
If you got ten years and 150K miles out of an automatic transmission, you got good service from it. Yes, many routinely do better, but those that do less aren't necessarily "bad".
Fun fact: The GM TH700R-4 was specified by GM to last 75,000 miles. When you go into one you can see how they did that and saved money in the process. Upgrades involve much in the way of upgrading sealing rings to longer-lasting Teflon one-piece, upgrading the critical apply pistons to a bonded-lip type, and replacing some of the critical wear bushings and thrust washers to bearings for modern drivers who put 2-3 times the miles on a vehicle than they did 30 years ago. Not to mention GM's own production upgrades like adding the aux valve body to make the 4L60, improvements to the TCC hydraulic circuitry, clutch packs, pump, and valve body and then the eventual upgrade to electronic control in several steps, then a case change, input shaft change, and more electronic upgrades. AFAIK they're still using the same basic unit today.