I live in northern NJ and purchased a Tamukeyama japanese maple about
a month ago. I planted it in full sun and according to the
instructions that the nursey gave me. I'm not sure if I'm watering too
much, but now the established leaves are starting to turn green and
the leaf tips are burning.

We had about a week's worth of 90+ degree weather. Could this be
causing the problem or am I watering too much / too little? Please
help!

water and then pick the brown ones off.

Toad