I am having an issue with my HP m551n printing out yellow backgrounds on color prints but not so much on regular prints or even internal test prints. I have changed out the yellow toner and also changed the ITB belt and secondary transfer roller, as well as installed a DC controller board and lifter assembly earlier for a separate issue. Would firmware or drivers be an issue since the customer is using UPD drivers instead of PCL6 drivers? Pretty stumped on this and looking for thoughts on it.