Selling 03 Chevy 2500 Dmax w/ Banks 6gun

Hi there, I'm about ready to part ways with my 03 Chevy Dmax and I was wondering what people out there would be willing to pay. Figured what better way to figure this out than ask people on this site who actually know about diesel trucks.
I have been looking at 09 GMCs and think I am going to go with one of them. Went to the dealer the other day and talked to them about trading in my truck. The manager at the place hopped in it and took it for a spin. They were willing to give me 14 for it. Pretty sure I could get more than that for it after looking at autotrader and the prices people were trying to sell them for on there, but if they were willing to come down to a price I liked I was willing to trade it in. I ended up hastling them for 2.5 hrs before they came to a price I liked. I signed the paperwork, the salesman left, came back 10 min later with different paperwork with a price 4000 dollars more and said he screwed up on the first price but this price wasnt much different. I pretty much laughed at him and walked out. Dont know who he is, but 4000 dollars is a huge difference in my book.
Anyway, about the truck. 2003 Chevy 2500HD Dmax LT Extended Cab 4x4. There are 108,000 miles on it. I had the leveling kit installed in Nov of 08. I had a Banks 6 gun bundle installed in Aug of 09. I have Sportsman Camo seat covers on the front seats and a DU-HA storage bin under the back. It has a Line X bedliner. The body isnt in perfect shape but it look pretty good.
What do you guys think?

The $14k that the dealer was willing to give was in my opinion a very good price. I looked at a truck almost identical to yours several months ago with the same miles but it was 2 years newer and could have got it for $14k as well. A more accurate place to find the selling price for your truck would probably be eBay. AutoTrader lists the asking price but you don't know what price was settled between the owner and buyer.

Why do you want to sell the 03? Did you know the newer trucks took a big hit in fuel economy due to the new fedrally mandated emissions standards. With fuel prices continuing to rise, you might consider this.