Just finished converting my 3760 to 34XX. There were a few 'hiccups' along the way and I wanted to help others out by sharing my solution(s) to save you some time in case you're experiencing my problems too. For the record, I used the 7.10 GCD to flash. All my issues had to do with Garmin Express.

1. Once the device became a 34XX, Garmin Express didn't register that the device took the 7.60 update. I tried updating, restarting, resetting, clearing NonVol, etc. The 'about' showed that the device was updated properly so not sure what Express was seeing/doing. Anyway, it only 'took' after I downloaded convert37x34.zip and extracted all folders except 37 to the SD card. I then re-started the unit with the card in place. Problem solved. 7.60 update stopped showing up as being required on Garmin Express.

2. Garmin Express would not update my unit to 2013.30 CNA. It wanted 4.3 GB of space - I had the Garmin 4 GB internal storage and an additional 8 GB SD card. More than enough. I was ONLY able to complete the update when I used Garmin Lifetime Updater, which was discontinued and replaced with Garmin Express. Couldn't find any setting in Express that caused this. Maybe someone else solved this another way?

When 2013.40 is released next week, I will try updating again through Express, but just note that Lifetime Updater worked like a charm for me.

JACKMAWATAN: Have you tried re-updating your maps using Garmin Lifetime Updater (assuming your original device was a life-time maps device)?