Have a Brother color laser printer (9340CDW) which has been flawless. A NAT recommended printer.

Have been using the original toner crtg's since new, but have back up new set. Last night it started streaking when printing black pages only. I switched out the black toner, shook it and ran the wire cleaner a few times, yet the streaking is still there. What is my next step?

Have kids which need printer to get 4-H projects, and homework printed out soon.