Hey Mate,
regarding the Sabretooth, I've had the same problem as well as some other Australian builders.
In simple terms, the Sabretooth can't put out the power needed for 4 motors (14.4V@19.2V in my case)
and the Reciever. Soo, you will need one of these:
an external BEC
that plugs in the way it tells you on the Sabretooth User Guide. (Has a picture of a Dimension Engineering
BEC connected to it, Fig.5.2 on Page 12)

Hope it helps