This is a pre 1995 unit with ford engine and standard controls as shown on page 3-34 and 3-35 2 years ago I had the same problem and replaced the inner parts and springs to the Main relief valve. pg 2-46 and 2-47 it still did no work with the new parts but then I cleaned out the hole and then all of a sudden it started to work. I thought there must have been a piece of dirt in the bottom. Now it is doing it again I installed a pressure gauge on the control valve assembly. The symptoms are the same on the ground and in the basket. We removed the main relief valve and cleaned the hole 3 or 4 times. then all of a sudden it worked for about 5 minutes. I get about 400 psi when I hit telescope out and it will work. But when I try to telescope in the pressure does not go up. (When it was working correctly the pressure would go up to 2000) I swapped relay R16 with R21 and I swapped R17 with R20. ( on R16 I have Brown-85, yellow -30, orange-87,org-red-86) The wire to 87 is not shown on the wiring diagram on pa 3-34. I have voltage to the bang bang dump valve but I did not measure the voltage yet.
Since it does this from both ground and platform controls you need to confirm if the bang bang dump valve is working or not, that's the first thing you need to do. And yes, insufficient voltage at the dump valve will cause it to not operate properly
Voltage was 13.23 volt when trying to retract boom on the dump valve solenoid red/orange wire. I also checked continuity in the brown wire to ground and it was good.
I would take a look at the wiring. This sounds like a possible grounding issue with the function valves. I don't know if all these functions are related wiring wise, but they could share a common ground. I had a similar issue where I lost the ground to one side of the solenoid bank, and I lost 4 functions in one direction. Just a thought. seems odd that the valve would be causing it in only one direction. That points to an electrical issue.