6 motor drivetrain not working properly.

[ElevatedCape255]

I just transitioned to using vexcode pro when we upgraded to a 6 motor drivetrain. I used this video to program it here
I transferred the code from nonexpert mode over to expert mode and added the 2 extra motors. When I go to change velocity, the robot drives forward and turns fine but when going backwards, it constantly goes back and forth(I am using arcade). When velocity is just default, the robot drives fine, except for when going backwards it just goes slow, WHAT DO I DO??

Robot configure code:

#include "vex.h"

using namespace vex;
using signature = vision::signature;
using code = vision::code;

// A global instance of brain used for printing to the V5 Brain screen
brain  Brain;

// VEXcode device constructors
controller Controller1 = controller(primary);
motor leftMotorA = motor(PORT2, ratio18_1, false);
motor leftMotorB = motor(PORT1, ratio18_1, false);
motor leftMotorC = motor(PORT9, ratio18_1, false);
motor_group LeftDriveSmart = motor_group(leftMotorA, leftMotorB, leftMotorC);
motor rightMotorA = motor(PORT11, ratio18_1, true);
motor rightMotorB = motor(PORT16, ratio18_1, true);
motor rightMotorC = motor(PORT15, ratio18_1, true);
motor_group RightDriveSmart = motor_group(rightMotorA, rightMotorB, rightMotorC);
drivetrain Drivetrain = drivetrain(LeftDriveSmart, RightDriveSmart, 319.19, 406, 306, mm, 1);
motor MotorGroup5MotorA = motor(PORT19, ratio18_1, true);
motor MotorGroup5MotorB = motor(PORT20, ratio18_1, false);
motor_group MotorGroup5 = motor_group(MotorGroup5MotorA, MotorGroup5MotorB);



// VEXcode generated functions
// define variable for remote controller enable/disable
bool RemoteControlCodeEnabled = true;
// define variables used for controlling motors based on controller inputs
bool Controller1RightShoulderControlMotorsStopped = true;
bool DrivetrainLNeedsToBeStopped_Controller1 = true;
bool DrivetrainRNeedsToBeStopped_Controller1 = true;

// define a task that will handle monitoring inputs from Controller1
int rc_auto_loop_function_Controller1() {
  // process the controller input every 20 milliseconds
  // update the motors based on the input values
  while(true) {
    if(RemoteControlCodeEnabled) {
      // calculate the drivetrain motor velocities from the controller joystick axies
      // left = Axis3 + Axis1
      // right = Axis3 - Axis1
      int drivetrainLeftSideSpeed = Controller1.Axis3.position() + Controller1.Axis1.position();
      int drivetrainRightSideSpeed = Controller1.Axis3.position() - Controller1.Axis1.position();
      
      // check if the value is inside of the deadband range
      if (drivetrainLeftSideSpeed < 5 && drivetrainLeftSideSpeed > -5) {
        // check if the left motor has already been stopped
        if (DrivetrainLNeedsToBeStopped_Controller1) {
          // stop the left drive motor
          LeftDriveSmart.stop();
          // tell the code that the left motor has been stopped
          DrivetrainLNeedsToBeStopped_Controller1 = false;
        }
      } else {
        // reset the toggle so that the deadband code knows to stop the left motor nexttime the input is in the deadband range
        DrivetrainLNeedsToBeStopped_Controller1 = true;
      }
      // check if the value is inside of the deadband range
      if (drivetrainRightSideSpeed < 5 && drivetrainRightSideSpeed > -5) {
        // check if the right motor has already been stopped
        if (DrivetrainRNeedsToBeStopped_Controller1) {
          // stop the right drive motor
          RightDriveSmart.stop();
          // tell the code that the right motor has been stopped
          DrivetrainRNeedsToBeStopped_Controller1 = false;
        }
      } else {
        // reset the toggle so that the deadband code knows to stop the right motor next time the input is in the deadband range
        DrivetrainRNeedsToBeStopped_Controller1 = true;
      }
      
      // only tell the left drive motor to spin if the values are not in the deadband range
      if (DrivetrainLNeedsToBeStopped_Controller1) {
        LeftDriveSmart.setVelocity(drivetrainLeftSideSpeed, percent);
        LeftDriveSmart.spin(forward);
      }
      // only tell the right drive motor to spin if the values are not in the deadband range
      if (DrivetrainRNeedsToBeStopped_Controller1) {
        RightDriveSmart.setVelocity(drivetrainRightSideSpeed, percent);
        RightDriveSmart.spin(forward);
      }
      // check the ButtonR1/ButtonR2 status to control MotorGroup5
      if (Controller1.ButtonR1.pressing()) {
        MotorGroup5.spin(forward);
        Controller1RightShoulderControlMotorsStopped = false;
      } else if (Controller1.ButtonR2.pressing()) {
        MotorGroup5.spin(reverse);
        Controller1RightShoulderControlMotorsStopped = false;
      } else if (!Controller1RightShoulderControlMotorsStopped) {
        MotorGroup5.stop();
        // set the toggle so that we don't constantly tell the motor to stop when the buttons are released
        Controller1RightShoulderControlMotorsStopped = true;
      }
    }
    // wait before repeating the process
    wait(20, msec);
  }
  return 0;
}


/**
 * Used to initialize code/tasks/devices added using tools in VEXcode Pro.
 * 
 * This should be called at the start of your int main function.
 */
void vexcodeInit( void ) {
  task rc_auto_loop_task_Controller1(rc_auto_loop_function_Controller1);
}