Could it be something other than the transmission. Is this a new build or something that just started. Are the motor mounts tight could it be an exhaust pipe close to something and the torque from 1 to 2 and 2 to 1 has it klunking? Do you still have the ears on the transmission? I will try to find a picture and post. Does it klunk harder if you get on it? Is your cross member tight to the frame? I don't know what it is just trying to come up with something.