Personally, I think you should do some block training. You could do a 3-4 week block of heavy weighted pullups to bring up your strength. Then, you could do another block that builds up the glycolytic-oxidative capabilities of the muscle you gained.
If you decide to follow this approach, there's an article at www.8weeksout.com
titled Secrets of Muscular Endurance
that outlines what you should do for the 2nd block. There's also a sample 6-week program written out on forum. To access stuff on the site you have to become a member.