I did a challenge twice this week, wasn't pull up specific but it would defiantly improve overall pull up performance.
It was 10x 100kg deadlift followed by 10 heaves
The. 9x100kg deadlift and 9 heaves
All the way down to 0 ...
Smashed your upper and lower back.. Not to mention your grip
Ends up being 55 chin ups and 55 deadlifts at 100kg
Ended up doing it in 9min 50