[rx4ur7]

You still have air in the cooling system.

Heat soak is an issue when you shut down. As long as air is flowing you are getting some cooling effect. Polished aluminum will not exchange heat as well as non polished. Steel and iron are going rise more and hold the most heat on a soak.

Lack of good air flow through the engine compartment will also cause temps to rise. But that would show in all conditions and get worse the faster you go.

A blocked or partially blocked exhaust will cause temps water and oil (when extreme) to climb on a incline. Leaking housing seal will also cause it. A FC3S just came in that got hot going up Mount Lemmon. Temps went up on the way up but were fine on the way down. When I checked it it is now pushing water.

From your discription of the gurgling I would do a bubble check, just to rule it out a seal issue.

Easy enough to do the bubble check for seals,
Start it up cold with the fill cap off.
It will push a little coolant out as it expands but once it comes to temp it will stabilize.
Let it get to full warm up.

If a seal is going - These guys will start with very fine bubbles, so small they can look more like dust. And there may only be one or two in 10 or 15 ses.
The next stage is there are enough that they form a foam.
Next bigger bubbles, becoming large enough that when they break you see combustion gas.
Last stage, blows water out as soon as you start it.
In the very early stages there will be no signs until it reaches full operating temps.

General Rule of thumb, You can be allowed 3 overheats (close to the mark) before $$$$.