Hitachi EX120 bogging issue

Hello, I could use some help diagnosing my excavators issue. I have a 1996 EX120-5 (serial# 1E4P053428) that has a bogging problem when the hydraulics are worked hard or multiple hydraulic control inputs at once.
Originally thinking it was a fueling issue as it would die at idle and would require hand priming before it would restart, I drained and rinsed out the fuel tank, blew out the supply lines and fittings, replaced the rubber supply line to the water separator with new, cleaned the...

Hitachi EX120 bogging issue