How does it work if you push a power that's sustainable. Like telekentic shield gives you armor bonus equal to your psy rating but if you push your psy rating is higher does it only stay maxed out with the push for 1 round and then drop down to your normal psy rating if you sustain it? If it's stays maxed out do you get a phenomenom every round you sustain it at a pushed level? or can you not push those powers you sustain?

I think it should stay as powerfull as when you manifested it. If not, pusing such powers would be quite pointless (unless you make yourself a timer after which the power level 'resets') and also you could fetter such power and wait for it to reach higher power level (over 9000!!!) after some time (again timer but an be abused more easily because you can cast powers out of combat and sustain them for hours)

You sustain it on the same level you manifested it, minus the penalties for sustaining multiple powers.

EDIT: Also, if it doesn't have any special rules regarding generating Phenomena (like Corruption powers have), you only generate Phenomena when you manifest, and sustaining will worsen any further Phenomena you generate.

You may sustain psychic techniques sustainable at Push level. But you may not push a sustained power. So you have to manifest it at Push level, then sustain it. Not the other way round.