thermostat temp 88 328 gts running too cold

My car won't get above 150 f when cruising and doesn't want to get above 165 f driving around towntown if I am at a long light it will get up to 185 f or 195 f It used to run hotter around 195 f to 200 f . I took the thermostat out and it starts to open at 155 and is fully open by 170 is that normal ? and could that be the reason I am getting a miss that comes and goes ? it seems like it runs better when it is cold out side.