Read over this post:
http://forum.ppcgeeks.com/showthread...85#post1290785
If you update to the new Sprint Maintenance Release ROM from 9/25/09 that will automatically upgrade your radio and the GPS problem should go away. Doing it this way though, installs a new OS so you will need to reinstall all your apps, which might not be a big deal if you have good complete backups. Also the new Sprint ROM adds a process that essentially breaks tethering by reseting the tethering registry entries. You'll need to run a .cab to resolve that if you care about tethering.
If you just update the Radio (also in the post referenced above), then that should resolve the problem, while preserving your existing install. You basically do an activesync, then run the .exe in the Radio upgrade package. It'll give you instructions and is relatively easy to do. I haven't run it on an stock locked ROM, but since it originally came from Sprint it'll probably be signed and work fine.
You can also try downloading the older xtra.bin file. Instructions are in the post referenced above.