Could be that 'Type 3 GTMxx' is only for the FM side of the GTM60 and doesn't update the HD Radio software however even more probably it's exclusively for the FM-only receivers such as GTM25-36. I have two 3597 units, one from NA with a GTM60 receiver OEM, and an AU with GTM36 as OEM. Both units received the 006B090100.GCD as firmware updates at some point, but only the NA unit had 006B154600.GCD onboard from new which is, i'm now certain, the firmware for GTM60 and probably updates both FM and HD Radio for it. As it was on the NA unit as OEM and Garmin have not issued any further updates for GTM60, you should be quite safe to add that file to RemoteSW folder to your 3590:
Code:
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If your refurbished NA 3590 came boxed with GTM60 [not GTM36] i'm only mildly surprised that the original GTM60 firmware was not factory loaded to the nuvi as it was with my NA 3597. Clearly it wasn't or it would be in RemoteSW folder unless it's been removed subsequently. Refurbs in the blue and white box often aren't properly updated by Garmin in my experience. Here's the file anyway as it's not available to download from Garmin according to the above link:
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