I have a quest vanquish and the rear deraileur isnt shifting properly.

it will go to the largest cog when its only shifter into 4th

it shifts from 7 to 6 fine, 6 to 5 fine, skips right to 3 then, skips to 1.

Ive tried putting a new shifter on but it didnt change anything, i cant shift past 4th

the derlaileur isnt bent nor is the hanger.

any help PLEASE? =)