Mine has a 5th in it also, and they definitely used it, and I most certainly don't have any trans damage. Just smell the dipstick for the tranny, if it smells burnt run like hell, if not (which it probably won't) do some more investigating. Another couple key spots to talk them down on, are oil leaks (just about a guarantee the area where the dipstick meets the pan leaks like a siv, not a big deal but you can make it out to be) another good talk down point is oil leaks that look like a rear main seal is out. 99% of the time, just valve cover needs a little tightening. The biggest thing is that when you start it, see how much smoke comes out the tailpipe. Mine smokes pretty decent for about 3 minutes on a 60 degree day, not sure if its normal or not but it seems fine to me. Flip the oil fill cap upside down, and put it on top of the filler. If the blowby pushes the cap off, walk away. If the cap simply vibrates off, should be a decent motor! check the differentials and the transfer case fill and drain plugs, if it is at a dealership then there should be no dirt in the allen holes on the plugs, and definitive tool marks from having to remove the plugs to check fluids. Another good area is the exhaust manifolds. bring a flashlight and look very very closely at the very last bolts on the exhaust manifolds (holding it to the cylinder head) if the ones closest to the exhaust exit look like they are melted, or are loose they definitely used that truck to pull, and they pulled hard. Those bolts being loose or melted indicate very high EGT temps, which are a big no-no. If they allow jack the front wheels up in the air and check the bearings by wiggling the tires side to side/up and down and if it feels like there is alot of play, bearings are likely needed ($300+ dollars each side) Other than that, its up to you to decide what you think it is worth. But these are all areas that I covered when I went to talk down my truck. I got a $10,500 truck for $8,000 from the dealership because I told them about all the repairs the truck needed that they missed and what it was going to cost me to have them all repaired. Did the work myself for $500 in parts.