Spektrum Rx voltage prob w/ Futaba RX

[Gee]

I'm starting to run into problems with my futaba 4pk & rs603ff rx. It keeps shutting down like the RX pack is low. The packs I am using are fine and fully charged. I do have 2 Futaba brushless servos for the steering and throttle. I guess they are pretty power hungry. I bypassed the switch and the problem still existed. I run a 2s lipo rx pack & UBEC in the savage XL with a Futaba rs604ff, but in the truggy the space is limited for running a BEC.

I heard rumors that the Spektrum sr3xxx rx can handle up to 9volts. Anyone know if this is true? It would be nice to run a lipo pack in there without a bec. Can a 2s rx lipo pack be used with the spektrum rx without a bec? Does it drop the voltage down for the servos?