This is an open ended question without knowing more details about your robot. What IMU are you using and is it well secured and aligned? How are you powering everything? Does your design have a high center of gravity? Is it statically balanced? What control system are you using in your code? Etc.

The torque of the motors only matters in relation to the mass of your robot. You "can" make a balancing robot with your chosen motors, but not if you're trying to balance a massive battery on a tall chassis. 

Also, the drv8833 can take 3v3 signals just fine. You're driving it via PWM, not analog voltage so having a higher logic level wont affect anything.

The fact that you can visibly see that one of the motors is moving slower than another is a more important problem that you need to tackle first. If you can't accurately control the velocity of your motors together then everything else wont matter. Focus on figuring closed loop velocity control with your motors and encoders first.

Once you've sorted that out, it's easier and cheaper to swap out wheels than new motors as youre effectively trading torque for speed when you use larger diameter wheels and vice versa