2006 Mercury 25HP 4Stroke not peeing

[Ajp9412]

Just replaced the impeller, boat ran fine for about 6-7 hours than the red light and sensor for over temp would go off. I’d kill the motor and start back up, beeping and light would go away but return within minutes. I also noticed that the motor also pees more at an idle and slowly decreases once I throttle up. At full throttle the motor barely, if at all is pees. Do I need to check the key on the shaft or just go ahead and replace the whole water pump? It’s a 2006 Merc 25hp 4stroke S/N 0R128101