Hi DRG,
I understand you have already done cleanings but recommend performing a Fixing Unit and Transfer Belt cleaning once again. Click HERE to perform a Fixing Unit cleaning. Click HERE to perform a Transfer Belt cleaning.
If the issue continues, take out the toner and rock it 5 or 6 times to evenly distribute the toner. Re-install the toner and attempt a print job. If that does not work, try another toner cartridge to resolve the issue.
If you continue to have difficulties, please contact our support group using the following link:
http://Canon.us/ContactLI