Head gasket or cracked head, your symptoms are classic signs of thatWell, i think its time to finally conceded to the overheating issue.
We had it fixed for 3 weeks, then its not been the same since.
Mikey and i tried several things today and cant rectify it. Only definite is when you go round a roundabout, you get heaters, and a normal running temp.
So options are to send the head off to be done and new gasket again, engine change, or set fire to it and replace it!