Dave, we ordered our 3670RL from HL with the Trailair king pin box. The dealer told me the driver who towed it from HL to Salisbury Maryland commented "it was the smoothest tow he did". I pulled it from there to home with a 2500HD and didn't feel any thumps it was really smooth. Then I got a 3500HD for safety reasons... Then the trouble started. There is now insufficient space between the TV & RV. HL is using a one down in size Trailair kingpin box. I have to give you the details so you don't have the problem I have. HL told me there were clearance issues between the box side rails of the NBS GMC 8' truck beds. Because of this they put a M15 instead of a LO5 Trailair. However, this brought my bed too close to the BH. The tailgate actually kisses the BH when I'm hooking up. Needless to say I have a big problem. Even though you do your homework and get the correct Trailair pin box per their chart you may still have a problem. I will attempt to attach some pics because a picture is worth...