I always sucked at high reps on pullups and chinups.
When I was rock climbing I could do about 12 perfect pullups at around 178lbs, but a single with 70lbs np.
Then I'd see guys that could crank out 20 reps, but still didn't have a higher single rep pull.
Try doing sidewinder pullups bro. These will humble most anyone. I doubt they are called this, but I saw a very advanced rock climber doing these and they are insanely hard.
Basically doing a strictu pullup to your left hand, then while in the up position bring you body sideways and touch your chin to your right hand and then go back to the left and lower. That's 1 rep. Then pullup to your right hand and repeat the same process to your left and so on.
If you can do 10 of these without kipping, while keeping your body controlled you'll be a pretty strong sob.
At the time I think I could do about 5 not quite perfect reps like this because it's actually really hard to keep your body at the top position while moving laterally.