It might help if you can scan a sample so people can see the defect and are genuine HP cartridges being used ?
I presume from your information the toner is not bonding into the media correctly , you might get some variance from one printer to another, even a few degrees in temperature can make a difference.
The fuser temp is located in the Adjust paper types menu.
Administration / General Settings / Print Quality / Adjust paper types.
Before making any changes I would print a menu map from both printers, you might find the one which appears to work better might have the media type set differently, instead of plain it might be set to Heavy or Bond, this would adjust fuser temp as part of the media change, it would also feed at a slower speed allowing the fuser more time to bond into the media.
If you print a menu map you will be able to recall the settings in case you change too many.
It might be you just need to try different media type to see which gives the best results, if you change a media type print a good quantity to ensure you get a good average before changing again.
You will notice if you change from Plain media type the print speed will lower as the media is now classified as custom type and the engine will slow to compensate.