That looks like an issue with the main drum, the unit is 6 inches in diameter and so you can get 2 copies of the defect on a page, the colours are seperated as the unit does not do a full rotation between each colour due to the gearing and the carousel moving, so you get each colour in turn one after the other.
As it's the full width of the image it might be the cleaning blade or similar within the drum unit, it might be worth checkign the lift remaining in case it's close to replacing anyway.
Replacing each cartridge won't resolve this issue, also the belt is not a likely cause as on this model the colour places are overlayed exactly over each other, the image is formed on the belt surface, the item that takes the toner from the cartridges and transfers it to the belt is the drum unit and it will exhibit this issue if faulty.
You should be able to confirm it by measuring from the start of one defect to the start of another, this should be 6 inches (152mm) - you should also see spacing between each colour of 6mm the image below is showing a typical defect if the drum has a mark on it, the image will show spacing of 6mm between colours, the spacing between the start of the black dot and the start of the next black dot will be 6 inches.
