I have managed to get it working on the VX6900. You definitely want to get rid of the GPS Enable for Titan cab. It is not needed and seems to be the direct cause of losing the COMPORT.
Make sure you update to the leaked Sprint Rom, and then if you want, back to whatever ROM you want. I'm using OMJ's Verizon OEM Rom right here:
http://forum.ppcgeeks.com/showthread.php?t=25335
Then I launch GPS Viewer, start with a Cold Start, and check the WAAS/EGNOS box (don't know why - read somewhere that it helps). Then I go to Google Maps, and click "Use GPS". Out side with a clear sky, usually comes in within a minute or two.
I've gotta search a little, because my Quick GPS program is still saying expired, and I know I read somewhere how to fix that. I think that will make things work a little faster. But as is, it is definitely working again.
Hope that helps...