I have a gd 77 and use it often in the South Florida area. If you still need some help with it, let me know.
Also, for info, sometimes, repeaters are set up with ptt instead of always on. In other words, in order for you to hear the channels, you have to key up the repeater. Most of the time, people will do this by saying their callsign, locale, and then Tac 310, etc, so that people who have monitor set to on will know what channel they are on without having to look at the radio.
So, a lot of the green light stuff you see is people who simply are bringing up the repeater without transmitting in order to listen first. If there is someone already on, they will wait until they id their station. That, and sometimes, it takes a little while for the repeater to sync up with the net.
That being said, in order to hear any of the traffic on the local system, you have to add the digital group to the rx group list. There is a good video on programming the gd 77 by a guy named 'razorseal' on youtube who shows the software and how to program it. He is in the WPB area, but the principle remains the same.
As I said earlier, anything I can do to help, and I'll be glad to. I really don't frequent this site, but I'LL check in a bit to see if you are still having any issues. The GD 77 is a good radio. It needs more on board memory for callsigns, but other than that, it works fine.