Congrats, OP! Your rig looks great!
As you have found, backing a fiver is quite a bit different than a travel trailer. It's important to remember that they are slower to react to a turn while backing, but turn quickly once they start so it is important to follow it around quickly. Further, backing a fiver in on the blind side is much harder than a TT because once the trailer starts to turn it limits your visibility severely, where a TT is further back from the truck and easier to see. All it takes is a bit of practice and you'll be a pro! :)