RFD900u with Arduplane very slow or doesn't connect at all

I have been trying to get a new RFD900u working on my plane for some weeks now and have narrowed it down to the ArduPlane firmware. If all the hardware & parameters stay the same then it works perfectly normally on ArduCopter, but either very slow to connect and download parameters (eg 5+ minutes, or it fails half way through) or doesn’t connect at all and says no heartbeat packets received on ArduPlane. I have rang RFDesign and gone through the SIK settings with them but to no avail. I have tried everything that I can think of to make it reliable but it’s just not working. If anyone has some tips, that would be awesome.

Kind Regards,

Perry