Problem facing when using Tank Mode

Hello, I am using XDC2230 to drive two motor, using mixed mode for tank steering.

I am using RC pulses to drive it at the moment.

What i am facing is: i can control two motor go forward with any speed, but for backward, i can only move it at very very slow speed, when ever i add up the speed, two motors stop. but when i go forward again, it resume normal.

also for left spin it function normal, but right spin it act like the backward moment, can only move at a very slow speed.

is there any setting can solve this problem?

Thanks,

I have checked, Firmware ID: Roboteq v1.3 RCBXDC 05/15/2014.

Do i need to update the firmware? if so, how can i do that?

Thanks,

I have download the update firmware, and go to the console tap and chose the update controller firmware via USB
when the Roboteq DFU Loader appear, it shown the Controller had been lost. and I cant update the firmware.

Please advice what other procedure I should do?

And i try to change back to separate mode, two motor can only move at once direction, but they can't run backward.

And whenever I drive the motor when it connect to Roborun+, the program shown "the controller is lost"

Understand the roborun + will lost connection to the controller, but when the dfu loader open up, what should we do to update the controller firmware ?
Thanks,