Hi Doug,
You might need to take a close look at your blades, it sounds like one of them is bent. It only has to be sightly bent to cause problems. If possible can you take them off and have a good look at them and if they are bent try to straighten them but most likely you may need to new ones.
My mower did be same thing so I don’t let my 17 year old son go near the mower again. I somtimes think that was his plan to get out of mowing the lawn.
Regards Noelene from Sydney Aus.