I'm with KD4UPL!! If you already have an '06 LBZ Duramax, you own one of the best pickups ever made!
No disrespect intended but your wife does not know trucks if all she's going on is that its not a new one.
If you do sell it, go for top dollar, that's one of the most sought-after diesel pickups in existence, to those who know their trucks. It's got a great transmission, the best injection setup, and the least emissions junk.
I think you'd be crazy to sell it and get a new gas truck. I'd sooner rebuild the motor and trans and keep it as long as I could.
People look for '06 LBZ Duramaxes.