The earlier versions of this trans suffered from what you are describing a lot, but that was mostly resolved by the time they got to 06, but it is still possible that is the issue you are having - the gasket on the valve body was not strong enough and it would blow out a spot that was related to providing the pressure needed to shift to 2nd gear. If you replaced the valve body (the gasket is glued to the valve body from the factory) right away as soon as you had the symptoms, you could save the trans, but most people lived with a mushy 1-2 shift until they just wore out the 2nd gear clutch/band so they needed a rebuild.