When I bought my 2013 F350 I tried all the usual things - just like you. I didn't like the results I was getting so I decided to try the Costco program. They ended up being the cheapest of the bunch. Just understand that you may have to travel a little to get to the dealership they use.
When I ordered the truck, I had a little discussion with the dealership salesman. I asked him why the Costco program got me the best pricing. He said that for all Costco quotes, he has to 'price aggressively'. He was the designated Costco POC at the dealership and he said that most of his business came from the Costco program.
