if its 07+ it will have 799 heads. if it has an electric TB it is a newer motor but if it has 862's its def not and 07 or newer. I dont know if the 4.8 came with 862's 07 and newer but i doubt it. Take this into consideration, if he insists its an 07 then he is lying or full of it. Who knows if its really a 5.3 anyway, you wont be able to tell. Sounds too fishy too me. Reason the motor was pulled in the first place?