Could my shoes be causing my patellar tendonitis?

Take your shoes to a good local running specialty store where they can look at your wear pattern, check out your gait and talk to you about the issue in person. Don't blindly follow shoe advice from someone over the internet.

I'm not a big fan of stability shoes. They've caused me troubles in the past.

Consider getting another pair of shoes with a decent amount of cushioning that allow your feet to land as naturally as possible.

Also, try to increase or decrease slightly the length of your stride on the side of the affected patellar tendon to see if that helps. And of course don't forget to ice the tendon after each run.

patellar tendonitis almost ended my running.

the solution for me was running in waffles, i.e. no more high heeled running shoes. took all the pressure off my knees and forced me to run correctly,

I had PT for over year and these exercises coincided with it going away and never coming back after I tried lots of other stuff. May be helpful for you and will be good for running no matter what.

Easier:

http://www.youtube.com/watch?v=z9wwf9NJz74

Harder:

http://www.youtube.com/watch?v=gtLSHGL1Ip8&feature=related

These are good too:

http://www.youtube.com/watch?v=2GLrKr54yA0

Hope that's helpful. What you are going through sucks!