Weight capacity is definitely your main cause when over loading it weakens the spring on your pressure relief valve casing it to bleed out and loose pressure
You should have 2 identical relief valves 1 for you lift and 1 for your curl
Simply swap the 2 relief valves around do not adjust them...
Stat test !
Does your coil have magnetism ?
When direct power is going to the coil check with a screwdriver or something metal to see if the magnet pulls by placing ontop of the spool/coil. 12volt
According to John Deeres website the 260E & 260D have a hall effect door sensor
I would check that first, you can bypass it with a piece of wire looped
Clicking sound when trying to crack over is starter solenoid in most cases.
Use a test light to see if you have power on the little wire while trying to crank if you do have power than you have a bad starter / solenoid
You should have a few in-line filters going to your pilot control body. Follow all the lines from the pilot control body until you find the inline filter. Open it up and use compressed air @ 120 psi and blow them both out as you don't know right or left. Google inline hydraulic filter so you get...