Lexmark T642 Slow Slow Printing

I've had this problem with the Lexmarks's T640 printers connected via USB to Mac OS 10.5.5 machines.

Problem: The Mac OS' default resolution of 1200 DPI for this printer causes the printer to have to rasterize the print job again AFTER it arrives at the printer. The printer does a painfully slow job of this.

Solution: Change the default resolution of your print jobs to "600dpi".

Instructions:

1.)Call up the printer settings menu by starting a print job and clicking the up-arrow next to "Printer" box.

2.)Click on the drop-down list with the name of your application and choose "Printer Features".
Change your resolution to "600dpi". Oddly, I find that "1200dpi Image Quality" is almost as fast.

3.)It might be a good idea to "Save as" this new configuration in the "Presets" menu at the top of your list.

You should notice a tenfold increase in the time it takes the printer to actually produce print jobs now.

Additionally, in the "Color Matching" settings (you can get there by changing from the "Printer Features" settings), be sure that you are using "ColorSync" so your printer isn't having to do any additional processing in that area.

Is the printer in sleep mode, then warms up when print jobs are sent?
If not try connecting to a windows laptop or pc to see changes, I work with Lexmarks haven't seen that one before, although sometimes they do seem to not print as fast as they use to (while printing).
you may also try reloading the driver for Mac.