It has nothing to do with VIN's and 08's are covered. It only specifies 05-08 Double Cab and Access Cabs and must be under manufacturers warranty. If you do not have the TRD package make sure they also upgrade all your shocks to Bilsteins.
Print it and take it in, it shows the old part # on the 3 springs that are on your truck, it also shows the new # for the new 4 leaf pack. Verify it when you pick it up, basically if you have 4 leafs then you are good.
They put a new set of 3 on mine and I had to take it back, they admitted it was a mistake and switched them.