temp will not get above second notch past 100 degrees then will go back down to just above 100, very little heat coming from heater after warming.

After running the motor for a while in the morning the temp will be just above 100 with some heat coming from the heater ( although not much at all) After traveling about 7 to 10 mile down the road there is very little heat detected at all. Temp gauge will go maybe to the second notch above 100 but quickly down to the first notch then travels between 100 and the first notch passed 100. From what Ive been able to find this car should heat to 195. How much dose this cool temp affect the heater out put and what can I do to fix this problem. Already did a back flush of heater core but not much difference at all in heater out put. Pontiac Grand AM 2.5