Over heating issue

Thank you for all the good info I am sure I purged the system when refilling the system I called Spar ten and they told me I could have a problem with the flow valve to the hydraulic fan it is an aluminum box mounted on the frame that has four lines coming in and out of it ..it sends fluid to the fan and power steering pump the steering line is seperart from the fan line they said to clean the values with brake fluid I am also going to add an external electric fan so I have a push pull system if that doesn't fix the problem don't know my next move down shifting is done when it gets hot cools it down enough to keep moving slowly but I want tow my boat and I don't want to worry too much about heat going slow is not a problem I want to get it right