I found this on another forum and it worked for me.
"I noticed while holding the phone in a certain way with the battery cover off, I would get a fix on all satellites almost instantly (using GPS Status). After some testing, I found that putting pressure on the piece of plastic between the battery pull tab and SD card was the solution.
With a little MacGyver ingenuity (folded a movie stub in half, placed on that spot, and put the cover back on), I now have perfect GPS reception, indoors and out.
I'm not sure if this is the issue for everyone with a Droid X and GPS problems, but it should at the very least help some."
I just did this and it fixed my gps that was intermittently working. Thanks
To the OP I am having almost the same exact problem as you! It works fine sitting in my house but as soon as I get out of my house and start driving I lose the signal, so irritating! I need to get this fixed I need gps for my work!