If you want positions, use something like
positions = zip(*np.where(test2D > 5000.))
This will return
In [15]: zip(*np.where(test2D > 5000.))
Out[15]:
[(4, 0),
(4, 1),
(4, 2),
(5, 0),
(5, 1),
(5, 2),
(6, 0),
(6, 1),
(6, 2),
(7, 0),
(7, 1),
(7, 2),
(8, 0),
(8, 1),
(8, 2),
(9, 0),
(9, 1),
(9, 2),
(10, 0),
(10, 1),
(10, 2)]