Thanks for all the ideas.

I am pretty confident that the thermostat is operating properly because it is the 2nd one (same result), and the temp always comes up to 180, then sits there for about 10 minutes (the tstat is 180).

The lower hose is corrugated stainless hose, and for sure is not collapsing.

The rad cap is opening up at 16PSI (2nd one just happen to have 2 good ones around).

I think it may be just the engine heat taking 10 minutes to heat soak the front of the intake (where the sensor is) right next to the tstat.

Good idea about the heat gun, we have one at work. Again, thanks guys for the opinions and advice.