I Think my Crown is Wearing Down the Tooth Below It. What Should I Do?

A properly fabricated and adjusted porcelain crown should not cause tooth wear.  Since you state you still have discomfort your bite may still be high.  Talk to your dentist about your concerns or find someone to give you a second opinion.

A properly contoured and adjusted crown should not wear down the opposing tooth.  This also takes into account that the rest of your bite is even.  It sounds as if you crown is still high in an area.  This should be adjusted so that contacts are even durning excursions (chewing mothions).  If your dentist cant figure this out, seek out a second opinion

There are several reasons why this can happen, but generally with a properly made, polished or glazed porcelain surface in the proper bite relationship there should be no effect on opposing teeth.  It sounds like you have seen your dentist about it a few times.  May be a good idea to search out a second opinion from someone with alot of experience in that area.  I'm not suggesting there is anything wrong with what was done, but hard to tell without looking at it directly so another opinion would be helpful.