3500-4500!!!? Damn, I wish I was even getting 10% of that. These printheads have a little over 200 ml put through them.
It can get frustrating trying to determine which print head is bad, as the drop tests performed through the machine can pass with flying colors even though a printhead may not be firing at 100%, causing the color shifts. One way to diagnose it, is to open up photoshop or whatever editing software your using. Most of them will have color changing options. Find one with the CMYK slider. Determine the color that's changing, and make a big square of that color. Than open the color editing tab and use the CMYK slider. slowly reduce one color at a time and watch the shift in color. If it starts to turn the color that is printing off, than you can assume that value (color) is the bad printhead in your machine. This may be a little harder to determine if its one of your LC or LM heads.
HP will warranty the printheads up to 1000 ml. You have to go through a song and dance before they ship them out, but they know the printheads are not as durable, and with the heating up and cooling down of the thermal printheads, it can deform the nozzles and cause color issues. If you get 3-4000 ml out of your printheads, god bless you. Atleast one black/yellow head went bad around 900ml, but when they checked the all pages, it was past the 1000 ml mark by that time. They still ended up sending me ALL the printheads, being the first two did not fix the problem as per a level 2 HP tech.
I know stock full sets of printheads for this reason. They're cheap enough.