I'm not sure why but on my previous 500 and 300 series lowrance units adding a mapping card did slow down the unit. On the HD i went into trails waypoints into settings and changed it from auto to 1 second it seemed to help a little but overall the gps on the HD is slower than previous models. I've posted on several boards and many folks have commented that their HD is very slow to react to boat movements. It is driving me insane.. its hard to get on a single tree top in open water with it like it is. Jason can you check your pm when you get a chance?