I have had similar experiences as the others here. I checked an office chair in box that was around 66 or 67". I checked it SFO-BOS then a week later BOS-IAH-DFW. Each agent asked what it was and then they took it to TSA for them to open and look at it. None of them cared about the size. I will way that the box was absolutely destroyed by the time I got it. To the point that the bag with the wheels and screws actually fell out on the conveyor belt. Luckily they made it that far.

I suspect you will be fine on the fee. I do also suspect that TSA will open it and look at it.