Are you using an airtronics Rx?? the reason I ask, is if you are using the RD6000 on a non ATX rx, you may have the RD6000 set for negative shift, and the VG4R may be a positive shift tx. Both transmitters must be set on the Same shift to work properly, I will add a little snippit of a post I received when I was trying to slave an RDS8000 (2.4 gHz) to a RD8000 (72 mHz) Tx.
"If you want to buddy box the two transmitters together you must use an Airtronics receiver. If you are using a Futaba receiver your master transmitter is modulating negative shift and the RDS8000 is modulating positive shift, therefore, it will not work. Both modulations must be the same. You cannot change the RDS8000 modulation. It will always be positive shift!
Please call us if you need further information. AIRTRONICS TECHNICAL SUPPORT 800-262-1178"
this might be pertinent info for you, as I imagine that the VG4R does not have selectable shift..
Hope some or all of this is helpfull.