Maybe too hot of sun, maybe too dry of roots, maybe too much water drowning the roots, maybe water in the heat of the day and steaming the roots.

Hum, Lots of many likely causes,but not all. Another could be: Is the JM cultivar you planted not compatable with the amount of Sun it receives at the time of day it occurs. Is there a passive radiant heat source too near the tree; so that, once the shade does arrive the heating affect is still being generated onto the tree. What about wind exposure. Has the tree's leaves been stressed by excessive, drying breezes?

If non of the above questions are true, then ask the question, Has a fertilizer been applied to the tree in the wrong amount, at the wrong timing, or proved to be the wrong kind.

You need to give more background information about the cultivar you planted, the environmental stress the tree is encountering, and in what kind of soil is the tree planted?

The one fact you did mention was that the tree was planted in the sun. Do you have a JM cultivar that needs more shade? If you planted the tree a couple months ago and the tree has just begun to show browning on the tips, a numbler of the above mentioned problems could easily be occuring due to the temperature heat-up and long hours of sun in the tail end of spring and early day of summer.

Thanks for the information, it must be too much water and too much sun. I drained the self watering pot and moved it to a spot with a lot less sun.