Air is an insulator so no, it wouldn't cause an increased temperature to be sensed by the sensor/sending-unit (depending on configuration). You would be surprised at how long air can remain in a block. Since it is relatively easy to check (front end of the truck up on a hill with the cap side of the radiator slightly higher than the opposite side, cap off, heat cycle the engine a few times while keeping the radiator topped up), it is worth a try. Worst thing is you'll spend a few hours as you wait for the truck to warm up, cool down, warm up, cool down, etc.

 

Most of the time, trapped air in the cooling system causes overheating.

You are assuming that any trapped air is localized to around the temp sensor.

 

You are assuming air is not trapped in there... Listen, I am speaking from experience with what I am telling you. Take it for what it's worth. I have seen the symptoms you are experiencing come from air in the cooling system. Air does not always cause over heating from my experience. It all depends on where the air is. In the newer engines, there is not a cross-over in the back of the lower intake manifold so air can get trapped in the back of the head affecting the sensor/sending unit that is used for the gauge in the dash.

Also worth noting. The radiator has NOTHING to do with the engine coming up to proper operating temperature in a properly functioning cooling system. It should always cool the coolant down well below what the engine actually needs to have it cooled to provided it is getting adequate air flow. The thermostat is in sole control of the temperature of the coolant in the engine. What you need to determine is whether the temperature is reporting properly or not...

I guess if you don't want to take advice and try something DEAD NUTS SIMPLE that will cost you nothing but your time, instead poking holes in said advice, I'll move along. Good luck with your problem.

 

Thanks for the well wishes.