A young client who has been following the course I laid out here has had some success.
He started with 2-3 good pullups before form broke down and he needed help.
Two weeks later he was repping 5-6 reps easily, and did a max set of 10,
A week after that, he has been getting easy sets of 10.
It's not rocket science, really - reducing "strength improvement" to "practicing a skill" is very effective for setting new rep records. GTG isn't ideal for improving maximum strength, but it's a very effective way to get more reps.