It's been a LONG time since I used my Onstar GPS so I can't remember the answers to some of your questions.
However you might want to become familiar with NMEA sentences. GPGSA tells you the # of Active satellites, GPGSV will give you their coordinates. As you can see you do not have that sentence.
I also think the Motorola format was Binary. I used the Winoncore software to switch to/fro NMEA. Here is a good link on NMEA sentences that should get you started
Ultimately my TTL converter died and I decided to purchase a new USB SirfIII chipset vs the Motorola SirfII.