Not sure which your GPS is because I don't know the number designation on any of them except for mine but if it is the Street Pilot it's just like my Garmin 295 ifor my airplane. Mine locked up too but at 120 knots when I was counting on it. I even had it sent back to Garmin who couldn't find anything wrong.
What the dealer told me (after he had more experience with it) is that it is not capable of doing all that it is intended to do because the RAM or it's equivalent gets over loaded, and when it does, it locks up. He had me turn off my WAAS and my track log. Since then it has been ok but that's been just a few hours of use since I did that fix. The other thing he said was that a data card loaded to the max can also cause locking up and suggested if the above didn't do the trick to deleat a couple of MGB.
Try it and see if that works. When mine locked up before, all I had to do was turn it off and start over. It even remembered what route I was flying. Nice instrument except for the locking up. Good luck, Bear