why will option 350 not work when i set it for the gas to cut on when outside temp gets to below 35 it cuts on when it drops below 45
How is the White wire from the heat pump wired? Did you leave it disconnected? If you have the white wire from the heat pump connected then it will turn on the furnace when the HP goes into defrost mode which could be fooling you, this will heat up the coils and may damage the system. If this is the case, disconnect the white wire from the HP.
I have the exact same thermostat and 350 works just fine for me.