That is the correct A/C belt for your truck (K040378).
You will also need to buy a large belt, and in order to find out which one you need you will need to find out what amp output your alternator has. I called the dealership with my VIN in hand and the guy was able to tell me (since I couldn't find it on the alternator case anywhere).
http://www.oreillyauto.com/site/c/s...431947&brand=Gates&cat=Belt+-+Serpentine+Type
If the rig is old enough then the alternator could have been changed already and the amperage stamp may not be correct on the one on your rig. Best to match it to the VIN or RPO code on glove compartment cover.