Toner darkness changes because of variations in print speed points, and the machine will go to slower speed points due to an increase in temperature. (This is commonly noted when printing on narrow media, with which the printer slows down after so many pages, or in hot environments: this is known as thermal slowdown.)
Therefore, if less toner darkness variation is required for a print job, you could set the printer to Quiet Mode, which runs 25 ppm. In this mode, the printer should not get hot enough to slow any further. To do this:
Menu > Settings > General Settings > Quiet Mode > Select On > Submit.
Please contact Lexmark Technical Support if you need additional assistance. NOTE: When calling for support, you will be asked for your machine/model type and serial number (SN). If you need help locating your printer's model type and serial number, click here.
Please call from near the printer in case the technician on the phone asks you to perform a task involving the printer.