After using this app for a while now, I've discovered that's it's no more than a band aid. You need to refresh the A-GPS XTRA Data every so often, to keep it working, and some times it doesn't help at all, like on a cloudy day.
Samsung has really dropped the ball here, and Sprint isn't offering any help either with this matter. Once I get enough time, I'll be attempting this fix, I found over at the Sprint forums.
" Here is my attempt at consolidating all the info required to apply the fix. This is the *non-root* version of the procedure. Hopefully this will help some of you. I cannot take credit for the procedure itself- there are many who have contributed to this and most of the step-by-step info is ripped directly from post 190, written by coasterphotos. I have attempted to update the links; of course credit goes to all the authors and techies who found/created the various files and did the work to make this happen- thank them for making this fix possible.
Again, this is what I did and it worked- I don't guarantee it will work for you or guarantee the links won't change. While I don't claim to be a hack of any sort, I am competent with my computer and tweaking stuff.
Good luck, hope this helps, and again, I claim credit for nothing except an updated link or two and a few minor, clarifying revisions to the steps. Anyone else, feel free to chime in with any edits.
1.) Download Odin3, ver. 1.85
Download Odin3 zip
2.) Download and install the Samsung USB drivers
Samsung (Click the "Software" tab, next to "Manuals")
3.) Download the GPS_FIX.zip (Thanks, Barlkon!)
GPS FIX for Gingerbread leak - xda-developers
4.) Place the GPS_FIX.zip on your phone's SD card.
5.) Download ACS Recovery (should be a tar file)
chris41g.devphone.org Use the file "ACSRecovery5-1.0.0.0-epic4g.tar.md5"
6.) Shut down your phone
7.) With USB cable disconnected, put your phone in download mode. (Hold down the 1 key on the keyboard and turn on the phone.) You should get a image of a little android construction guy with a message to not turn off target.
8.) Plug the phone into your PC with the USB cable and wait for all the drivers to install.
9.) Open Odin - You should see a com port listed under the first box on the left if drivers were installed successfully.
10.) Uncheck all options.
11.) In the PDA section select the ACS tar you downloaded.
12.) Click on "Start"
13.) You should get messages indicating the operation was successful.
14.) Disconnect USB and remove the battery.
15.) Reinsert the battery and enter recovery mode (hold down vol down + camera + power until you see the recovery screen). (If your phone boots into the OS, you will have to reapply CWM as it will be overwritten during boot of the phone)
16.) Use the arrow keys on the physical keypad to select the option to apply zip file from sd card (not update.zip)
17.) Select the GPS_FIX.zip file you saved on your sd card and apply it.
18.) Should say it was successful and then you can select the reboot option."