Your swapping of receivers just verified that the receiver is not the problem.  You could continue swapping components like that to check for voltage drop.  Some other component could be pulling voltage down, and StarFire is just first to raise a caution.

Do you just get this during the moment when you are turning the wheel, to disengage steering?  Do you have to fight the wheel a bit to disengage?  That high current draw from the ATU motor could be causing a voltage drop.  Are the 12V lines on this system getting close to 13.5V when the machine is running?