I replaced mine on my own without dropping the engine/trans. The total time from start to finish was approximately 5 hours taking my time and not rushing it. The part cost me about $135 at my local Pcar dealer.
You can confirm that the AOS is faulty by removing the oil cap. The car could stall or you will be able place your hand over the opening and feel the suction.
My comments and instructions are included on the following thread:
My AOS adventure... - Rennlist Discussion Forums