That's the bottom radiator hose, actually hoses...there are two of them. I just replace them on my truck as well. The coolant hoses on this truck typically leak at the connections to the engine, which is why the updated hoses with 2 o-rings have white ends where they connect to the motor. If yours is leaking at the radiator connection (it appears be), and if the motor-half of the hose doesn't have the white end on it, then get both the bottom hoses. In addition to that, I replaced the upper hose as well, since it wasn't the updated version. I would suggest the same...if it hasn't started leaking yet, it will before long.

FWIW...on the half of the lower hose that connects to the radiator, I would almost be tempted to just change out the o-ring and clean the radiator fitting real real good instead of getting an all new hose - but only if I was positive that is where the leak is occurring, and it's not the radiator itself leaking coolant onto the hose or something like that. There isn't an updated dual o-ring version of the lower hose that connects to the radiator and that one doesn't usually leak like the others so a new o-ring might be all that is needed. The downside is if you're wrong you will have to re-drain the fluid again and mess with it again if the new o-ring doesn't do the trick.