Since both the lift and tilt are weak, that makes me think the BICS valve may be having problems. If your machine has a BICS valve.
I've never worked on an 853 but I know the later models had a BICS system. "The BICS Valve combines hydraulic lift and tilt lock features into one valve. Early BICS systems used two separate valves". The BICS has an electric solenoid valve that opens the path for inlet oil to open the lift and tilt valves. So something could be wrong with the solenoid or valves. Also, both the check valve and solenoid valves in the BICS have screens in them as an oil filtering function, these could be clogged.