You are confusing the Cellular and WiFi.2.4 & 5GHz bands are the Wifi and have nothing to do with the broadband.
Also, don't worry about what someones calculated coverage map says, because it's meaningless for this... What does the 'S' meter say? If the device is bouncing around like that, wither the Jetpack is in trouble, or your coverage stinks because thats not what it's supposed to do.
Put it up next to a window and look at the Rx level. Better yet, find the menu that shows the actual receive level.. It should look like "RSSI (xx)% (-xxdBm)" and report back with the value of "xx" That should be a solid number and in the 80's or less.
