i had one injection pump die on me when i had my 97 tahoe 6. 5TD. it died from a failed optical sensor inside the pump i think @ 20,000km. that was the only injection related problem. engine lube oil cooler lines were a weak point, they decided to leak at the crimp seal between the rubber flex & aluminum hardline pretty much on the clock at 35,000km [i had it fixed once, then i just wrapped the lines with shop rags so it didn't drip on the driveway the next time they started leaking] mine was the l56 version of the engine which had an egr system that worked terrably. it would jam up, which would plug up the cat on it. this happened a few times, and after the last time i had it fixed at the dealer, i "fixed" it myself for good when i put the 4" straight pipes on it, and custom made a 1/16" solid aluminum gasket for the egr valve. a sub. has the l65 version which has no egr system, but still has cat. . trans will be the 4l80e which is a very nice trans [electronic OD version of the th400] rear brakes need to be manually adjusted as the "self adjusters" didn't work real well i think. the PMD was the weak point on the injection pumps, but there were pmd [aka fsd] cooler/relocation kits avalable to keep it cool, and removing the plastic "turbo power" cover was also useful from removing heat from the pump... oh, and if the front end hasn't been greased at every oil change the idler arm might be toast. it is a pain to get at [you need to drop the front plastic splash shield] and is often forgotten. [iirc, there was 10 or 11 points plus the slip on the front driveshaft]
i ran mobil1 15w50 in my 6. 5TD and did oil changes about every 6000-10000km and it used about 1 liter of oil between oilchanges, but the oil cooler lines were weaping... changed 3 rear u-joints out [one under warrenty, 2 myself], castrol syn 75w90 front/rear diffs. mobil1 atf in trans/t-case... hmm, i miss my old tahoe sorta... it was a nice truck