Radiator cap - should it be pressurized?

I am working on my '74 Duster. I am running a factory radiator and over flow/reservoir. It normally runs at 180 degrees... which is when the thermostat opens. The last two times that I have taken it out... it has climbed up to 195/200...

My thermostat opens at 180 like it is supposed to. I have not lost a head gasket, both the coolant and oil are clean and clear.

On my way home today it got up to 200 on the highway. I pulled off at a gas station and let it idle to cool off. What I noticed was that at 195 degrees my upper radiator hose was soft like there was no pressure in it. It eventually crept back down to 180 and I eased it back home.

I am using a 16lb Stant Lev-R-Vent radiator cap. When I got home It was back up to about 195. I tossed a rag over the radiator cap and gently pulled up on the lever only to find that there was NO PRESSURE behind the cap. I opened it up with it running varified that the coolant was flowing.

My question is, Shouldn't there be pressure behind the radiator cap in that situation?