I do just want to clarify that I have no affiliation with Motorguide. I'm just trying to help out a fellow fisherman.
Well.. the last thing I can think of is this. Do you know which heading lock mode you have yours in? Course mode or compass mode? The reason I ask is that if you have it running in Course Mode, the Xi5 is going to do everything it can to keep you on a straight line path between point A to point B. So if wind or current is blowing your boat left or right off of this course, it's going to do everything in its power to stay on those preset GPS points. Your boat could be facing into the wind but still, be pulling you left or right depending on where your point B is located.
The compass mode just goes from Point A to Point B. It doesn't matter if it blows you 100 yards off course, it just heads towards that Point B. So you could get more of a circular pattern while in this mode. The reason I bring this up is because if you are setup in Course mode, it could potentially work that motor a lot harder trying to stay on that line.
Some examples of this below. I hope you get it figured out. There isn't much worse than spending that kind of money for something that doesn't function correctly as advertised. I'm sure the techs have asked you for your serial and confirmed that this isn't one of the older models of their unit that needed some sort of firmware update with a dongle. I thought that was my problem but with mine being newer, the serial number showed that mine was good. Although I didn't believe them since I was having the problem, the Lowrance settings clearing and recalibrating of my Xi5 fixed my problem.