The high levels powers are the trickiest part of balancing the new psion that we have come across.
Here is a thought on how to help balance them. If a character uses a power which costs more power points than their current manifestor level, they cannot use another such power for a number of rounds or minutes equal to the difference between their manifestor level and the power points used.
Alternatively, they can't use another such power for some set amount of time. Maybe an hour.
Thoughts?