Got a new GPS. Now BT doesn't crash!
 

I was trying to connect my GPS and 770 using USB as a workaround to the bluetooth crashing problem. When I couldn't get a connection (in host mode), I tried connecting the gps to my laptop and that produced lots of unrecognised device errors. So I sent my old gps (the £40 device from MobileFun) back and they sent me a CellLink BTG-7000 instead. I was initially upset because this device doesn't have USB, but I thought I would try it over bluetooth and it's worked perfectly. I have done a number of two hour journeys with it and the only problem was when the 770's battery went flat. I now have a car charger.

The only real difference I can see between the two devices is that my old one ran at 38400 baud and the new one at 9600 baud. So I would guess that the 770's bluetooth stack is locking up trying to process the higher data rate.

So to pose the question.
What is the baud rate of your bt gps and how often does crash?

For me:
38400 baud - crashed after 5 to 30 minutes.
9600 baud - hasn't crashed yet.

Technically, the NMEA standard fixes the baud rate at 9600, but I think most GPS receivers allow higher-rate connections. I use the iBlue receiver, and its specs say "up to baud rate: 115200 bps". I have no idea what baud rate it is actually using, though.

I have seen the BT drop, but only very rarely. I have seen it go down after 45 minutes, and I have seen it last for an entire 2-hour trip. I have never seen a pattern.

Personally, I highly doubt a baud rate higher than 9600 is really going to buy you anything in terms of functionality, because the data that is being pushed is almost definitely not enough to saturate a 9600-bps pipe.