I'd consider the trade in tax allowance if your state has that. in WA you only pay the difference between trade in and purchase price.
also, Jimbox is correct in a lot of ways to me. I had an 07 with 5:13's running 37 BFG's and it was better than stock but didn't feel as torquey as the 12 to me(of course I have the Rubi and not running 37's now.
I would say do it, but decide between trade in and private party sale based on your states tax/trade in policies.