Okay, here is what I did and I think i got it working right. Before when I went to upgrade Nav, it said that it didn't recognize my phone and I had to pick from a list of devices to get the APK. After downloading the right one, it would work the first time and then if I tried to open the app again, all I would get was a blank screen.
I went into Applications and scrolled down to Sprint Navigation and clicked on it. Then clicked on uninstall. After that I powered down the phone and booted into recovery. From there wipe/factory reset, then reboot. When I got done re-syncing with my gmail account, I opened Sprint Nav. When asked if I wanted to upgrade, I clicked on upgrade, and wasn't told that my device wasn't recognized (woohoo). When it finished downloading the APK, I clicked on it to install the update. Then exit out and reboot the phone.
Since then, it's been working fine and it still says V2.8 Premium.
Hopefully this helps with anyone who was having the same problem that I was.