HP3800 has blurry text

Hi, dont know what the previous person means by developer as that is usually the toner cartridge and you have changed this. You need to do a test sheet and stop it before it gets to the fuser. By doing this you will be able to establish if blurring is occurring before the fuser or after passing through the fuser. My experience with this has been that it is either the toner cartridge or a fault with the fuser assembly.

Hello sir; Sound like you change a lots of things but only one important item you missed it that is developer, try again!