The 4L80e is very strong in stock form due to the center support being anchored down in the rear planetary. You really don't have to upgrade internal hardparts for anything, unless you are boosting it. Even then, there's plenty of guys beating on their junkyard 4L80e with twin turbos and having fun. And the hydraulics are very simple and reliable. Only a few valves really need addressing when rebuilding them. Otherwise it's just gaskets, seals and bushings. They really didn't change much on the design either, so it makes the rebuilding easier. I've rebuilt a few myself and I would say they are pretty straightforward. The 4L80e i swapped in my 99 Silverado was a junkyard unit and all I did was put fresh fluid in it. Unknown mileage, lol. I beat on it with the "little" 5.3.
The forward clutch-to-clutch shifting design is the way to go in my opinion. No forward band that wears out like the 4L60e. The 2 bands on the 4L80e are only used for reverse and and engine brake. Some folks don't even get those changed because they are still servicable on teardowns and rebuilds.
OTOH, the 4L60e has something 30 common failure areas, from hard parts to hydraulics. Well, that's what I've read, I've never been inside one. The thing is, by the time you upgrade all the internals with aftermarket and expensive Sonnax parts, you've got yourself a huge bill, and sometimes even those units fail. It probably doesn't help that they were so many changes during production years, but those changes were to improve on failure-prone areas.
They way I've see it is: I'm broke and can't afford the 4L60e...or would rather spend money on something else. Just my opinion though.
