New Truck Buy or Lease?

When I had agreed to purchase after all the haggling on my trade. I was looking at all the numbers I told the fiance guy I wanted to take over night and discuss all the purchase options with my wife. I figured we could think out our purchase options clearer and see what fit us the best with out an audience. During one of my conversations with the owner of the dealership on leasing he told me the leasing companies amortize the diesels trucks at the same rate as gas vehicles. They just lump them all together. But diesels don't deprecate at the same rate as gas trucks they retain value longer. He said typically you can purchase at the end of lease and capture some equity that just goes back in the leasing company confers if you turn it in. He said we (the dealership) used to buy out all the diesel leases that we could ourselves when people turned them in and then resell them to grab that equity. The leasing companies got wise to us and put a stop to it, they wanted those $$$$. He said typical that equity is $5K to $10K at the end of the lease on a diesel if the vehicle is well cared for. I asked if I could just purchase on paper and trade right back in and lease another and capture that equity. He said you sure can I got a lot of people that do just that. I am not sure I buy all of that, but something to consider at the end I guess.