i am working on a Cat DP40KL the truck has had slow/weak hydraulics it happened about 6 month ago good pressure input to the spool valve assembly. replaced main pressure relief valve and issues were resolved. about a month ago the truck lost full hydraulics pump seals were blown pump was replaced and hydraulic service was done. about a week ago the truck started to have slow and weak lift again adjusted main relief valve no change swapped out valve still have issues swapped out spool valves and still have the issues. all mast functions are effected steering is good but to use lift,tilt or side shift you have to floor it and still moves slow truck is a 9000lb capacity and will barley lift 4000lb right now. any ideas of where to go would be great help.