Just wanted to make sure you did not try to maiden it without the engine

I think that enough pressure is the key to safe retraction. If it does not retract well @ 120psi, the cylinder/ geometry is not right IMO.
I use 120 psi in all my planes and like to use large and maybe even 2 large air bottles so the pressure does not drop that much when retracting.
I always test the system @ 140-150 psi regulary so I know it will hold up and use 120-130 psi normally.

To have induvidual exhaust flow control, the UP valves all have it. I am going for an UP-3 mechanical sequencing valve in my Hawk.
If you don't like the UP valves, you could also go for the normal red Robart valve that also have seperate up/ down exhaust control and a sequencer.

Robart valve: http://dreamworksrc.com/catalog/prod...roducts_id=746
UP-3 valve: http://dreamworksrc.com/catalog/prod...roducts_id=740