I've had my 06 for 18 months, only have about 24K on it, runs great, tows great, just a pleasure to drive. It took a little to get used to that 6th gear synchro angle, but now I don't even notice. Only problem I had was the rail relief valve, warranty covered. I went to taller tires, decreased RPM's at freeway speeds. My seat has been fine, few long trips of close to 4K, the material is a stain magnet if you don't scotchguard it well. My a/c works perfectly, nice and cold and blend door is right on all the different settings.
I have no idea what they are going for, bought mine new. I do know they are becoming more and more sought after because so many do not like the EPA stuff on the new trucks. You should be able to get the extended warranty on it, that's a good idea since you don't know how the previous person took care of it. If you are buying from a dealer, make it a bargaining chip for the sale.
I'd buy another one, love the 6-speed, great truck.
CD