Do I understand that you are making decisions based on the stock gauge with an unknown source sender? May I suggest that you not do anything until you actually know what temps you are working with?

As to the belching of coolant when shut off, big blocks (and Hemis) have always heat soaked. Either put an overflow bottle on it or leave the coolant down an inch or so in the radiator. In my humble opinion, that is not indicative of anything other than it's a big block Mopar.

At any rate, if you want to throw $10 or so at the Water Wetter, go ahead. But that in not gonna fix any real problems.

Get an accurate temp gauge and sender to determine if you actually have a problem and when. Then, remember this good rule of thumb; over temp at hiway speed is typically a water flow problem while over temp at slow road speed is typically an air flow problem. It is also a good idea to look at the water pump housing bypass hole and size it down if excessive. It allows hot engine water right back into the incoming cool water.