It sounds to me like a contact problem....... especially since you have already moved the nock point so much....

Are you using a string loop ? (for your release)

You should LIGHTLY spray the vane area and shaft in that area with foot powder..... let it dry and shoot the arrow at a target. Retreave it and look for anyplace that shows the powder being scraped off..... this will show contact problems..... Another thing to try (if ya can) is remove the cock feather from one arrow - so YOU KNOW there will not be ANY vane/feather contact.... then shoot through the paper - if you see a dramatic improvement - BINGO.... you will then know you have a contact problem......
I went through the fire trying to tune my bow 2 years ago.... I did a LOT of reading on the subject so I know what you are going through !

Tom