If this was my tractor I’d verify that the pump shaft is turning with the engine running before changing the pins. If the shaft is turning then something else is wrong. Possibilities include, plugged filter, plugged suction line, bad charge pump, sucking air at the suction line or charge pump seal, check valve, relief valve. If you have Hy-Tran in it maybe a glob of the waxy stuff it forms from water blocked or plugged the filter. You are sure it has enough oil in it. Just tossing out other possibilities for you to consider.
