ZX160 slow and weak

[Huffa]

Hi, we have a Hitachi zx160 11000 hrs on clock that has lost a great deal of speed and power in all attachments. Still travels ok on flat but weak up hill. Hydraulic oil temp gets hot too on a hotish day, up to 90 degrees or so. Pumps have been pressure and flow tested and passed easily. Of note is that when oil is cold first thing it barely moves, doesn't even want to click into second gear, once oil temp gets up to about 25 degrees it starts to come right but still lacking pace and grunt in all attachments . Also when the travel is put under load like climbing a hill, oil can be heard bypassing/hissing somewhere from behind or beside the cab hard to tell. Not sure where to go from here, the professionals have had it and carried out all the test they say its not the pumps but cant tell me whats actually wrong . I'm nearly at the point of shelling out on a new pump but am still concerned it may not be the entire problem . Any ideas would be appreciated

 

[TNB]

What series zx160? Did this happen at once or gradually? Did the professionals check pilot pressure and verify it’s in spec?

 

[Huffa]

Its the first of the Zaxis 160's, non common rail. It came on quite quickly but was hard to detect for while as was doing light work but it has got worse over the last few months, is not inoperable but is not a fraction of the machine it was and is to the point where it needs something done. Pilot pressure and pump control pressure in spec