I don't think the location of the tower is moving. In my small expiriences with WiMax on my Tri-Fi hotspot over the past couple of years has been that the power is being turned down and the allotted spectrum is smaller than before. I believe it now only works in 5 or 10 hrz. If indeed those two factors have occured (are occuring), the strong signal area before will no longer be strong.
Suggestion going forward, upgrade to a triband device. Currently, you can get the SG4 at bestbuy for a $1. crazy. If you upgrade to a triband (or even a dual band iphone 5s/5c), your region has great sprint service. Tampa is already a Sprint Spark network. Well good luck.