From a Mitchelle trans mission manual for Mercedes trans. Keep in mind the same transmission is on gassers. So don't be thrown off when you see something like fuel pump relay which is on gassers. I have not read of any sort of relay on the diesels.

"WILL NOT UPSHIFT
Incorrect governor pressure. Defective governor assembly.
Check for stuck kickdown solenoid or for constant voltage to solenoid
caused by a defective fuel pump relay or sticking kickdown switch.
Valve body dirty or valves sticking. Repair or replace valve body.
UPSHIFTS AT HIGHER SPEEDS THAN SPECIFIED
Check pressure control cable engagement, condition and
adjustment. Check for stuck kickdown solenoid or for constant voltage
to solenoid caused by a defective fuel pump relay or sticking kickdown
switch. Check governor pressure. If regulator pressure is too low,
replace centrifugal governor. Ensure control pressure regulating valve is operable."

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84 300D, 82 Volvo 244Gl Diesel