just do more pullups !
you're doing 18 now so add to your volume.
let's say you want to shoot for 3 sets of 8.
1st set: is in the bag.
2nd set: you bang out 876543 and stall, so jump up or use a box and do the slow controlled negative for 2&1.
3rd set: you hump-up 876 and kill for almost 5 then switch to the negatives for 4321 and you're out.
try that for 3 weeks then lighten up. come back a week later and you'll have it.
then shoot for 50.
now quit wasting your time looking up articles and go do it.