I have a similar problem with my FD20-6, I also cleaned the strainer but no change. I went on to check the pressures on the torqflow transmission at the forward and reverse ports, I have no pressure other than an intermittent 20psi in reverse at which point the truck does try to move but it is not consistent. I think my oil pump needs replacing. I removed the engine (Isuzu) but I cannot separate the torque converter from the transmission, do you happen to know how the torque converter is removed? Does it just pull off the input shaft? If I can remove the torque converter I can examine the oil pump. Thanks, Bob