Hmm. I've noted in my area that trees growing near the canal do the worst. They normally start off really nicely, then about 2 years in start to decline. Sometimes pruning trees can cause a decline too, as it removes the nutrients stored in leaves.
The youngest leaves look like they have a potential nitrogen deficiency.
My knee-jerk reaction to that would be to do 2 things:
- Give it a high quality slow release fertilizer with micros, possibly with nitrogen
- Hit it with copper on a regular basis. In my yard, I found that Cu was lacking, especially along the canal. After a couple of years worth of 75% copper (the highest concentration I could find), the trees bounced back nicely.