check if there is a solenoid on your pumps.
there maybe one (standard) or possibly two ( 2nd is an option for variable loading )
if you have variable loading there will be a dial in your cab with a symbol of your arm and arrows. this dial varies the pumps via the controller (c-1) computer.
if you have a solenoid, turn your kpss back to on, usually the chromed toggle switch is down for "on".
turn key to "on" position, do not start the engine, go back to pump comp, undo wires conn, with a digital volt meter on dc volts, read by conn to both wires what the voltage is -> should be 24 vdc.
then with wires still disconn, turn your meter to check ohms and read the coil of the solenoid -> should be 15-30 ohms.
the pf solenoid & opt variable loading is powered via the computer for horsepower control thru the two 1 amp fuses.
when you turn off the kpss "release", the power comes thru another fuse and thru a current limiting resistor sending a constant miliamps to the solenoid partially destroking the pumps but not near enough under load. thats why she lugs the engine down.
let me know your results.
also let me know if she tracks straight or tracks to one side?
if this checks good i'll need you to guage into various pressure test ports on your pumps and by running some circuits stalled over relief i should be able to narrow down from there, better at that point to do over the phone.