Here's my experience with my xv6900. I got mine the first weekend they were available, I've been modifying it since the Alltel ROM procedure got stable. I'm running the 3.37 Alltel radio and a cooked ROM from the PPCKitchen 3.02 ROM. I have full GPS, I know this because I went to a VERY rural area where I had no cell service. I did, however, get 4 to 5 satellites for the GPS and did get a position. Of course, Google Maps couldn't do much for me because there was no data connection to download maps, but I did get a position through GPS Viewer.
Just a couple of things I'd recommend you check:
1. Verify your External GPS settings in Settings and verify they are COM4 and Harware are set to none, 4800.
2. Go under start-settings-phone-services-location setting and verify that it's set to LOCATION ON instead of 911 ONLY. GPS will not work on 911 only.
To me, it sounds like you didn't get true GPS since it didn't come up until you got a stronger cell signal... sounds like you got triangualtion. Of course, I'm fairly new to this myself to I could be wrong.
