If you are dependent on 4G WiMax coverage, you only have two options:
Keep the EVO and wait out LTE coming live in your area
Get a LTE device now and get a WiMax capable MiFi (which have really come down in cost)
I hope you are legally using the hotspot. Because if you plan on hacking your Hotspot for LTE, you may be disappointed. Sprint is anticipated to block unauthorized tethering with their LTE network, or at least limit it for people who are deemed excessive users. Also, Sprint only has unlimited data for smartphone usage. Sprint does not offer unlimited hotspot plans.
Robert