The leaves exhibit a pretty classic example of chlorosis. There can be several causes for this, not all of which are dorect results of nutritional problems. Too deep planting and poor drainage can cause it, for example. A full cup of Hollytone is excessive, but this slow acting fertilizer is very unlikely to be the culprit in what you're seeing. The best thing you can do is to first check the soil pH. If, however, this 6 foot plant has been in the same location for some time, that's probably not an issue. Further soil testing would probably be necessary unless you can think of some recent change that may account for what you're seeing.

Thanks for your comment. Tested pH at a few spots around the plant and it is in the 5.5-6 range. Plant has been at the same spot for 15 years at least. Whats interesting is that i have another similar deciduous azalea of the same size and age doing very well right next to this one.

Will submit a soil test and keep you updated.

Even though my pH meter is decent i find the results quite different from a professional soil test. Will be interesting to compare the results.