Does your Owners Manual or Service Manual have any towing specifications in it for your truck? If not, then Google can be your friend. I typed "Silverado 1500 4x4" in Google's search box and got a lot of conflicting information. The NADAguides.com web site states the Max Towing Capacity is 5,500 lbs. An answer to a "Question people ask" has a much different answer: "The 2011 Chevy Silverado 1500 can tow up to 10,700 lbs. with the 6.2L V8 engine and MAX Trailering Package." Of course, your Silverado may not have that particular engine and may not have the MAX Trailering Package, so check your Owners Manual, Service Manual, or data sticker for the towing capacity of your truck.
The more important question, however, is can your 2011 Silverado 1500 4x4 STOP a flatbed trailer with your 10' NCO Alaskan on it? You will have to install a brake controller in your Silverado and properly wire it to your trailer to have the truck and trailer brakes work together. IMO, stopping is more important than pulling.