LaserJet Printing

Hi, 

I have a Colour LaserJet Pro M252dw that I bought in January. At first I had no problems, the colours were as expected and then all of a sudden it started printing everything really dull, the colours were no longer vibrant and all blacks were jet black. I'm a pet illustrator and use a lot of varied tones to create portraits - especially when the pet is black I need different shades to create the shade and highlights - so I need it to be true colours.

I've spoken to HP and they tell me it's my iMac and I spoke to Apple and they tell me it was my printer.. 

So Far I've tried:

• Resetting the driver
• Reinstallation
• Remote access from HP Support where they changed settings for over an hour with no luck
• Printing from 3 different devices
• Checking my display settings
• Changing my documents colour profiles
• Printing from different programmes

So far nothing has made any steps in the right direction.

I have the original cartridges which are genuine and again, I bought it in late January, brand new from the Apple Store.

I'm pretty computer savvy but I am running out of ideas of what is causing it to print such dull colours, I have printed out the "test page" from HP that has a hot air balloon on and that seems to come out perfect - I did print a "Print Quality Page" however that I don't think looked right.

If anyone has any ideas please let me know as I'm desperate to get it corrected as I have commissions I need to post and hate having to send people a sub par product.