First of all, make sure you have the garmin technical specification for the gps35, this is different from the datasheet and the quick start guide.The NMEA 0183 document would be helpful to you too, it costs money to get it from NMEA,but if you do a search on google you can find it for free.This is the standard in which nearly all GPS units communicate,it details the NMEA sentence structure and baudrates, etc.The usual problem with communicating with GPS recievers is the ASCII format.
Make sure you send the "$"
Followed by the command "PGRMO"
Then a ","
Then the output sentence you want to disable
Followed by ","
Then a "0"
Followed by a carriage return and a linefeed,All in ASCII characters at the default 4800 baud.It will echo back exactly what you sent, if it echos back something different, there was an error in what you sent.This will disable the output sentences one by one, leave the "$GPRMC" command,this will contain your position and time info.It will output the $GPRMC every second at 4800 baud.You can also change the baud rates and how often the sentence is transmitted, by the "$PGRMC" and "$PGRMC1" commands.Or you can turn off the "$GPRMC" too, and re-enable it every time you want location and time info.