Have you given any thought to replacing the camshaft sensor?
What is(are) the OBD II code(s) that you are getting? The MISFIRE codes for all cylinders can be from the cam position sensor, so I suggest you get the cam position sorted out.
A misfire is defined as, "the expected work was not performed." A single cylinder misfire would be caused by factors unique to a single cylinder, but you have misfires from all cylinders so you should be looking for failures that have a global affect, such as the cam position not being reported properly so the ignition timing is wrong.