@angelozip
Thank you for your explanation about the limits of a GTM.
Although your experience is with the GTM25,26, and 35, I have read the GTM20 is the same as the 25, the only difference being the connector to the GPS mount. The GTM25 has a mini USB connector, the GTM20 has a wider rectangular plug.
My GTM20 is the newer type, shorter and has no lights like the older model.

Regarding the key suggested by others using the old jetmouse 4 digit keygen, using FID 1527, many say this does not work.
I did generate keys for both Navteq & TTN using 1527,0,0,1 and entered into Nuvi.
I'm hoping if I generate new key using 1527,0,0,0 it will remove those subscriptions, WILL THAT WORK?
I will go ahead and generate keys for all subscriptions (0,0,0), then new ones with 0,0,1.

Another problem I’m having is resetting the FM table. I see 8 entries, I then hit “Reset”, it clears all the entries, then slowly they come back, one by one.
No new ones, just the ones I had cleared. It seems they are stuck in the GTM20’s memory. HOW CAN I FIX THAT?

You said “if you do not receive channels TTN, or key signature is incorrect, incomplete or is not compatible (update the GPS and GTM20 firmware).
I am able to update the Nuvi 765T firmware, BUT WHERE DO I GET THE GTM20 FIRMWARE? I was unaware the firmware is available.

My last two questions
1-If a GTM’s subscriptions are properly recognized, can you connect it to another GPS that has a compatible connector, or must it remain with the one that generated the keys. Perhaps the Nuvi’s firmware is taking information from the GTM20’s firmware and changing things.
2-On several occasions I had entered key codes from my desk rather than have the GTM20 plugged in the car.
By connecting the AC charger it enabled the Traffic feature (GTM20 attached) and I was able enter codes just as if it was connected to car. CAN THIS METHOD OF ENTERING CODES CAUSE PROBLEMS?

You state “Try unmark the Navteq from the insert page / signatures “, this is not possible since the Nuvi 765T with USA/Canada does not have that option to select different carriers.