I have towed twice that with both a 2012 6.0 with 3.73's and a 2015 with 4.10's and the 6.0L.
The motor screams (cant hardly hear it in the 2015) at those heavy weights but it has the strength to do it. The 6.0 more than holds it own against the other two HD gas trucks in real world towing. 11K is not a problem for that motor. The 6.0 is about as bullet proof as they come. I liked running that motor.