I am in South Africa and has recently bought a Disco4 which soon afterwards developed a problem of shuddering on low speed of between 40km/h and 50km/h when you gently press the accelerator and does the same in high speed when it must select a lower gear to gain power on an incline. when it does it and I shift it manually to Sport the problem seems to reduce or go away. the first diagnosis was dirty gearbox oil which I was told would require a flush but upon doing that discovered that the intercooler was leaking water and some water got into the box or something, so it was sent for a torque recon but the problem persists in spite of the torque convertor having been replaced 3 times. what could be the problem and solution?