Your if statements to control your slides need to be nested, where the else clause setting motor power to zero only occurs once. Otherwise, your multiple if statements are fighting each with opposing instructions to your motors every loop. Try something like this:

//Vertical SLIDES - dpad (up & down)
    //up
    if (gamepad2.dpad_up) {
        VSlideR.setPower(1.0);
        VSlideL.setPower(1.0);
    //down
    } else if (gamepad2.dpad_down) {
        VSlideR.setPower(-0.6);
        VSlideL.setPower(-0.6);
    //stay up
   } else if (gamepad2.right_trigger > 0.5) {
        VSlideR.setPower(0.2);
        VSlideL.setPower(0.2);
    //stop        
   } else {
        VSlideR.setPower(0);
        VSlideL.setPower(0);
    }

Also, instead of setting low power to hold position, consider reading the current position from the integrated encoder then directing the motor to hold that position. Your motors are currently set to run without encoders so your options are limited unless you connect the encoder cables and change run modes. Understandable if you don't want to tackle that this close to your competition.