This should work for you, but it's untested as i don't have a 3750/3760 to try it. I've converted the patched rgn file to a gcd file and changed the Software Version to 501 from 500 which should allow you to update via microSD card.
Spoiler: Download and Step by Step instructions

1. Connect your 3760 to a PC and look in .System folder for a file named GUPDATE.GCD. If it's there delete it. It may be there or not depending on how you last updated the firmware. [If you can't see the hidden .System folder, go to Folder Options in Control Panel, select 'View' and then select the radio button next to 'Show hidden files, folders and drives'].

2. Extract Garmin.rar onto a CLEAN and otherwise empty microSD card: [Only registered and activated users can see links. ].

3. Ensure the unit is CHARGED and is fully OFF, not on Standby [if in standby, press and hold the On/Off button for several seconds until you get the option to turn it off].

4. Insert the card into the unit and then turn it back on.

If this is successful, on boot you should see 'Loader' appear on the screen after the startup Logo. Leave the unit complete the update and then remove the card. You should then have the additional features enabled.


IMPORTANT: Before you do any firmware flashing ALWAYS backup your nonvol region 41 [see first post for link to tutorial]. Make files back up of the internal memory and then clear nonvol also as per guide in post #1 . Do that again after the flash as well.