Need help, overheating at cruise rpm

[midnightrider1818]

So, i have a 85 searay 250, mercruiser 260 350 with a alpha one gen one, last year at the end of the season I started to overheat at cruise, i came back in and all fine, boat sat in well for probably 3 weeks and when I went to to take it out I noticed my temp gauge was up after being on plane, back to idle and all good, cleaned intake ports on drive and no difference, anyways I think I found my problem, about 3000 rpm the water starts to pulsate coming out of the transom to the thermostat housing, i put a new water pocket cover on and sea pump impeller but no change, however I did not change the bottom base but seen nothing wrong with it, i have a video here of what it is doing, this to me makes sense of why it's creeping up while on plane but now I am lost as where to go, i also scoped out power steering cooler and no restriction in there, I ran a wire thru transom tube going thru back of boat, anybody have any suggestions

 

[midnightrider1818]

Also my video it says file to large to be uploaded

 

[midnightrider1818]

Here is the video I don't think it should do this

 

[midnightrider1818]

Also I do want to make sure I'm looking at this right, I should have more water flow with higher rpms, it should not break up like that right

 

[Bt Doctur]

seen that before, assuming your in the water in this video. The base gasket is leaking and your sucking in hot exaust at higher rpm`s because the water pump in the lower unit is above the water and the cavity is empty except for the hot exaust gasses