Hitachi EX60-2 slow & weak hydraulics after 30-40 mins

Hi all, I am hoping someone can help please, my EX60-2 is playing up again, firstly the engine dies under any load put on it. I believe I have cured this problem by replacing all the fuel filters and fuel line. I now have a the following problem, when i start and work the machine from cold it functions fine, both tracking and hydraulics. As the machine warms up and gets hot it is fine for about 30-40mins, then the speed and power of the hydraulics starts slow and become weak, selecting...

Hitachi EX60-2 slow & weak hydraulics after 30-40 mins

Hitachi EX60-2 slow & weak hydraulics after 30-40 mins