Ask the dealer what "out of pocket" means? One of the key questions is what is the "Capitalized Cost Reduction", that is, the money down???
$4k out of pocket is dealer-speak and it's bullshit - don't let them get away with it. Get a firm break down of what the fees are. There is bank fee, first month, motor vehicle (by the way if you're buying the truck out of State there is NO MOTOR VEHICLE FEE because you're registering out of State), and then down payment (cap. cost reduction).
By getting a breakdown you can really determine the true monthly lease payment. What you would do is take the down payment (cap. cost reduction) and divide it by the 24month term of your lease and then add that amount to the $640.
Also, get them to take out the Taxes so you know what the monthly amount is. Get a base number for the Truck with nothing else added to it. Then, if you want cap cost, add it to the price (in your head) to get your TRUE figure. If you want to finance the taxes instead of paying them upfront, fine.
Here, you are not paying for taxes as part of your "out of pocket". WOW. That means that AT LEAST 2k of the 4k is down payment.
Insofar as a lease "saving you money", versus buying, it's true that you have to pay costs each 2 to 3 years, but it lets you get into a much higher priced car for much less than buying it outright. In general, the lease is designed to have you pay the depreciation for the term of years you drive the car. The big downer is that each time you start a new lease you have to pay taxes again and bank fees again and inception/end of lease fees. So, it may end up costing more than a new car if you're the kind of guy who buys ever 15 years.
Also, the mileage costs .25cents per mile over the alloted mileage. If you're not going to drive 24k miles in 2 years go with the 10.5k option. It will save about 20bucks a month on the lease.
Finally, the dealer is not doing you any favors at $640/month with that amount of money down. He can do that same deal (on the 2007) for $540 if not less.
Good luck. It's an awesome truck . . . . . . .