Well, kind of hard for me to advise at this point, you mention the engine is struggling at low speeds after slowing it down, does it struggle at high speeds as well? Do you slow the engine down because it seems to be struggling, then notice the hot exhaust leg? Any other signs of overheat, such as burnt/discolored paint on the powerhead?
Have you done any cooling service to this engine? If not, I would recommend pulling the powerhead and water pump, the water pump should be serviced regardless of the current conditions.
Post some pictures of the powerhead (with engine cover removed), perhaps someone might notice something. It is hard to describe how much water/spray should be coming from that outlet, it is a mix of exhaust and water spray. It is not uncommon for the exhaust legs to get hot on some of these engines as well. There is no dedicated cooling water telltale on these engines.

Just reread your post, and don’t quite remember your original post…Was the exhaust leg discolored like that before, or did this occur after running it? Did you have the powerhead off? Perhaps you have the wrong base gasket installed. I can see the bottom of the cylinder head in the picture, it does not appear to be discolored.
I know it is a pain, but try to recap your previous post for us, or let us know if you find it…D

Barely visible, I think this is the spray hole

upload images free