If you're a Costco member go through their auto program and you'll likely get the best price out there. In shopping recently I found the prices would range from between 79-82% of MSRP.
Also, I'm curious about your trade-in being close on KBB & NADA. The 06 Duramax I tried to trade in was valued at 14,500 on KBB and 19,700 of NADA. Of course, the dealer wouldn't budge over KBB and said NADA was irrelevant. A friend who works in the car business said dealers have some influence over KBB and the trade-in values are low and the retail number are high. The benefits the dealers on both ends... of course.