Hard to tell from the photo, but make sure that your filter housing/assembly is up to the pump capacity, and also that the pump is not running faster than intended (thus creating higher gpm). I think most pumps are rated at either 1.8k or 3k.
Reduce flow restriction and reduce heat.
E.g., I run a 13.6@3k gear pump on a log splitter, and with the recommended filter head w/3/4 pipe fittings(rated to 20gpm), the oil got too hot. Upsized filter head(inlet/outlet are 1.25?), and the fluid temperature dropped dramatically.
Too many pipe adapters may affect flow, and from what I understand, high pressure hose restricts flow more so than the equivalent length of high pressure pipe.
Also, fluid capacity should be, I think, 1 to 1.5x pump gpm.
(Not a hydraulics expert by any stretch of the imagination).