LT3999 Synchronous Rectifier and higher output current

Hi there

I'm in the process of designing a power supply using the LT3999 and have a few questions:

1.) Can you recommend a synchronous rectifier  that could be used with the LT3999

2.) Is it possible to enhance the output current capability? (I need 5.5V@3A @Uin=15V)

3.) When simulating with LTSpice (15V Uin, +-12V Uout) changing the output current will change the output voltage, is this normal behavior?

Simulation file: www.mediafire.com/.../file

Thank you very much!