GPS is 100 percent useless on my phone... does not work in vehicle at all.

I experience the same problem. "Hey, I'm driving on the same interstate road for 2 hours and then WHAM, "You are now off track", and I look down, and I'm apparently driving in the lake a mile away!"  It's so maddening. Happening as I near my destination, it renders the program USELESS, and I wish i'd printed out a Google map beforehand instead.
Because of the vehicle-discussion - I have a Ford Ranger.
Phone Signal is often strong.
Instinct tells me "Your GPS signal is weak".

Ok, I have very little to say about my experience at the sprint store.  Essentially, I was told there is nothing wrong with my phone (I love being told that I don't know what I am talking about).  The woman was willing to get me a replacement, however it will not be new!!  I think I now understand the issue though.  It seems that some phones have better GPS reception than others (from the sprint store employees mouth).  My wifes phone is absolutely perfect, my phone, not so much. 

Long story short, if you are having trouble with you GPS, you are basically out of luck.  Try to take it back and get another one to see if it has better GPS reception.  My "new" phone should be here tomorrow so I will write back then and update. 

This should really be a easy fix, I don't know why they have not done anything to fix this issue. I ride a motorcyle and can't even use the gps or pandora on my phone using a stereo bluetooth headset or speakers because of this. I went to the sprint store today and tried out the new palm pre paired with my bluetooth speakers and they WORKED and it was really LOUD, I was able to use the gps and have music playing in the backround, it muted the music everytime it had to prompt me for a turn. If this doesn't get fixed soon then I'm gonna have to go with the palm pre, it sucks because I really like this phone.