Print is lighter in middle of page than the rest of the page

Could be a number of things causing this.

Try cleaning the charge wire to do this open front cover and by the waste toner bottle their is a green tab grab this pull it out until it stops and push it back in. Do this several times.

The optics could be dirty I noticed it said prints up above Do you actually mean prints sent from computer or copies. If it is prints from the computer, it might be the developer unit. If copies than turn the unit off and take off the platen glass clean all the mirrors you can slowly move the lamp assy to the side to give yourself room to reach all the mirrors. It will slide back to the home position when the unit is turned back on. Use windex on a paper towel to clean the mirrors.

If you have any more questions just ask. I am a certified on this model and most others.
Hope this helps.