Unfortunately there's not a whole lot you'll be able to do. Since more than just you in your area are experiencing this, and you've already tried multiple devices, and lots of people here are having zero 4G problems, it's a solid bet that it's the service in your area. Maybe there are a lot of people on the 4G network. Maybe the network isn't totally ready yet. Tampa, Florida is just one place in the US, and Verizon is working on rolling out lots of new networks and expanding current networks pretty regularly.