$$ Advice - 2015 Silverado LT 3500 SRW crewcab 4x4 w/ Diesel

I am spoiled. for years I make an offer based on the invoice of the vehicle I want or plan to buy. In fact that is the first thing I ask to see when buying. based on the invoice I make an offer and tell them how much I want for my trade in and then I let them think about it for a week. if they don't call back I move on to the next dealer. one dealer here in town sell trucks for $500 over invoice every day of the week. he sells a lot of cars and trucks this way.