Buying a used vehicle and with trade in question

I would sell my used car myself. You will get more if you sell it yourself

Markup on a used vehicle is all dependent upon how bad the previous owner got screwed on a trade in. You could see a markup range of anywhere from $1k to $6k on a used vehicle. Usually it does not get to around the $1k range until it has sat on the lot for 90-120+ days when they are looking to dump it.
Edit: You will never know the markup amount unless you have someone on the inside at the dealership. You have to negotiate it yourself, as opposed to knowing the invoice price on new vehicles.

Come up with the following before you go in:

1) Amount you want to pay for the "new" truck
2) Amount you want for your trade in
3) Treat both as separate negotations
4) Do not visibly fall in love with "new" truck
5) Be willing to walk away

Obviously you have your range of 27-29k, but that's a big range. Book it out on KBB and Nada but keep both of those numbers in your pocket until negotiating later, if those numbers help your case. Make sure you are armed with information on the vehicle before you go in. Also, your range of 6.5-9k on the trade is also big. See #2 above.

They are a business and have to make money, but if you go in without information on that specific truck and your trade in then they will make $7k off you when you could've easily done $4k-5k better than that.