Wrong Encoder

You're using the encoder internal to the motor. You'll want to be using the through-bore encoder. Use getAlternateEncoder() instead of getEncoder(). This will disable the limit switches coming in from the through-bore encoder and all should be well.

In drivetrain change the following:

mLeftEncoder = mLeftMaster.getEncoder();
mRightEncoder = mRightMaster.getEncoder();

to

mLeftEncoder = mLeftMaster.getAlternateEncoder(AlternateEncoderType.kQuadrature, 8192);
mRightEncoder = mRightMaster.getAlternateEncoder(AlternateEncoderType.kQuadrature, 8192);

You will also need to make sure the switches on the through-bore encoders are set to quadrature.

Hope this helps.