Out from under the shed may be good enough. I see that you have a 3D Fix but in Mississippi you should also be picking up the WAAS satellite and so it should have been showing as "Enhanced". that would have dropped the EPE (Estimated Position Error) number and the speed should not bounce around as bad. Make sure that you are not around any trees, buildings or mountains and see if the numbers look better (the lower the HDOP and EPE numbers the better the accuracy will be and the less the speed will jump around).

You should also check the power supply tot he unit as we have seen low power (voltage and/or current) do this too. No loose or corroded connections between the unit all the way back to the battery it is powered from. Don't forget to check the fuse, fuse holder and battery contacts too as these are sometimes overlooked.

If none of this helps; call the Humminbird Customer Service folks. 1-800-633-1468