I went through Costco and ordered exactly what I wanted. There is no need to compromise and buy what the dealer has in the lot unless there is a BIG discount to do so. Costco got me fleet rate and the experience was very pleasant; dealing with the fleet manager instead of the bottom feeder salesmen/vultures circling the driveway entrance to the dealership.
My salesman gave me a web link and special # to enter after I logged on. I could 'watch' my truck as it made it's way along the assembly line, load onto the train, travel to California and finally on the truck to the dealer's. Pretty cool...