Hi James,

If the lifting speed is normal when cold but becomes very slow when hot and under full load, I would first check the hydraulic system rather than the electronics.

I would compare the hydraulic pressure cold vs. hot under load and check whether engine RPM remains normal when the fault occurs. A pressure loss when the oil gets hot could indicate internal leakage, a pressure control/relief valve issue, or possibly the hydraulic pump.

Are there any fault codes stored when the problem occurs? Also, does the same problem affect other hydraulic functions when hot?