OK George, so now you're assured that there is nothing wrong with your unit hardware. As to flashing to 3490 'without all the thumb pressing', i suppose you mean without having to flash the logo for 3490 using updater.exe? If so, yes but this time we need to follow everything to the letter so go back to Post #1 and do each step [including the NV Backup before you start the conversion]. Then flash the complete 34 fw, following the instructions down to this:
At this point your Nuvi will restart without logo but as a 34xx.
Go to volume page ,get Debugging menu and reset Nuvi again (clear non vol), restart it and go to Debugging menu again.

Go to MTP Settings and set it to Mass storage mode.
NOW... AND THIS IS IMPORTANT TOO: Backup NV again this time as 34 for another safeguard. Then do the folder restoration stuff detailed in 'OUTDATED METHOD' after 'Restart your Nuvi .' Then you skip down to the last part of Post #1 to:

CURRENT METHOD:Another way to convert 34xx with logo and enable features :

Flash full 34xx firmware
Unpack the file to an empty SD card, turn nuvi off, insert card, turn nuvi on.
remove sd
You've already flashed the full 34xx firmware, so now you can just do the SD card thing again [see note below] with no fumbling around trying to find that 'elusive G-spot' [umm, heard that before somewhere ...]. This is where i think it all went wrong for you before so before you start let's check something: In the pack you dl'ed named 'convert37x34.zip' which you should have unzipped to a microSD, open the folder named '34'. In there is 140.bin file. I want you to check something in that, so dl this zip file [Only registered and activated users can see links. ], and open Mod3xxx.exe. Browse to the file 140.bin and check what it looks like. I'm particularly wanting to confirm that 'ASR' is checked like this:
iitr

If everything is the same as above exit the application. If one of those isn't checked, then check it and hit 'Save'. If you want the Android Phonelink, check the last one too. Now I want you to check something else: Garmin>Updater>1376>Ldr.bin. Open Ldr.bin with RGN_Tool and check the SW Version. If it's not the same as the fw version your used to flash [i.e. 7.90], replace it by loading the 7.9 fw into RGN_Tool and saving its boot.bin as Ldr.bin to replace the version in the 1375 folder [you've probably got 7.20 there at present]. This may not be all that important but do it anyway to be consistent. NOTE: Don't use that big card again. It shouldn't be a problem but I've never used anything that big for this kind of thing, i've only used 1, 2, 4 and 8Gib cards. 32GiB [and even 64Gib SDXC cards re-formatted in FAT32] are fine in modern nuvis as map cards though.

Now you're ready to flash the 34 logo and enable features so make sure the unit is fully off not just in standby, then put your card in and turn on. Let it finish, it will reboot. Then check if you have the ASR Icon in Apps. You may need to restore the ASR/SRX files for your map and the en_US.srd for Jack & Jill and for another voices you use [if this works, you best use en_AU.srd with the lovely Aussie Karen for a while ].

Let us know how you go .... Good luck this time.