Say it with me, c a v i t a t i o n.... Willy is right your losing pressure due to the fluids *cough pun intended* fluidity. When you go up hill the fluid level stays level with the ground and it goes away from the pickup tube in the trans. Im not aware of anyone that makes a deeper pan for your trans offhand but Im sure there is one out there. Id just cut it apart and add 1 1/2-2" to the depth and the pickuptube.
