I'm not sure what's wrong with your plant at this point. I can think of some vague possibilities, but nothing even close to definite. Is there a possibility of posting pictures? Also, have you thought about posting in the Shrub Forum (with pictures!)? I'd really like to know what you find out, so please post here if you do find an answer.

Other things that might help....
1. What type of soil do you have?
2. How is drainage at that location?
3. Is the effect evenly distributed through the plant?

I have semi-clay soil but with medium rocks mixed into the garden bed. Drainage is excellent. Yes, it seems to be evenly distributed, but not throughout the entire plant, about 3/4. I think it is winter damage, but maybe something else....

Here is a link that might be useful: {{gwi:240991}}

That looks like winter damage to me. I'd be surprised if Gardenias are winter hardy in Knoxville. What zone is that?

I think we are 6b or a 7...