[btwilson86]

Are you running a properly mixed coolant (50/50 antifreeze to water or similar?) Less antifreeze and more water will mean a mixture that boils at a lower temperature, which can cause increased cooling system pressure that can cause the cap to open lower than you would normally expect it to.

Your coolant temp reading bothers me. Unless someone put a VERY cold thermostat in the car, it should be reading higher than that at operating temp. My car has a 180 thermostat, and at operating temp it is just a little under the halfway mark on the gauge. The water temp sending unit for the gauge is usually after the thermostat, so it will read warm water once the thermostat opens. I think if I were in your situation, I would test (or rather replace) the thermostat, and check for proper operation of your water pump (assuming you have a good mix of antifreeze/water).