The signal circuit is a parallel control circuit that allows the highest load signal to up stroke the pump
A signal (resolver valve) valve that is leaking will stop or slow the pump upstroke. Because the valves are in parallel. all the functions will be affected to some degree.
To test it is best to operate and hold the function that is not working correctly and then in turn operate all other functions and see if one function makes a difference. That is usually the problem valve
If it is only the lift functions affected I would suggest that the lift compensators valves and or there seats are suspect
Also don't forget to operate the steering as it also has a resolver valve and has been updated quite often over time