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.
1990 ¾ ton 4x4 Chevy Suburban
-Cummins Diesel - 12 valve - factory rebuilt
-6 speed bullet proof manual transmission - NV5600
-Gear Vendors Overdrive
-Upgraded Holset HX-35 turbo
-NP205 iron transfer case
-3.73 gears
1982 ½ ton Chevy Suburban
-6.2L diesel - high nickle crack free 1982 block
-Stans headers
-Ported heads
-Timing gear
-4 speed automatic
-3.08 gears
-30 mpg on freeway