Try out some single rep chins held in the contracted position for a TUL ( time under load ) of around 30 sec then fight the negative to conclusion ( x 1 weekly only ) , then try increasing by 2.5 - 5 lbs per week over some 6 weeks , Im sure you will se a difference. The single rep allows full concentration and effort.
I tried this over a 6 week workout programme and documented my results by video ( you tube ... see below ) and I increased/doubled my chins from 50 lb - 110 lb for similar TUL ( 45 sec )
All said/done if you do not allow for suffice recovery from any exercise regime then progress will be non existant , after many years of training ( now age 45 ) I know that I can only train a particular lift ( & any musculature involved in that lift ) every 9 days , otherwise I see regression in resistance and/or reps.
video; Week 6
Best wishes , T.