If you go with a GMT 400 there are a few things I can say about the maintenance on mine.
- Shaking Fuel Gauge - Was told by several people this is caused by a bad sending unit and it is time to replace the pump. I have done this twice and it still shakes. More looking into it is the stepper motor that is bad on the dashboard. It works it just shakes. So if you see this I wouldn't stress about it.
- Power Steering Lines - K2500. I had this happen while out hunting. They decided for a cooler to run the lines from the pump down the frame, in the frame, and finally back up to the steering box. Mine rubbed against the oil cooler lines and started leaking 2k miles from home. I would check these and see if there is damage and if not maybe put a rubber sleeve over them
- Intake issues - Gather the later Vortec engines (mine) leak antifreeze from the intake. Mine started once again 2k miles from home. I have kept it topped up on coolant but looking at having it done.
I went in knowing some of these are just the normal ownership. The first two caught me by surprise. I replaced my pump (it was the original) and I still had a shaking gauge. Frustrated I left it alone for months till I went to fix a gas leak and it broke during removal.
Overall it has been a great beast. I have taken it camping several times, towed a trailer to Colorado and back with it. While it was in Colorado we fit two elk inside of it, and a tarp can easily cover up the back. I don't use the 3rd row but have when my family is in town. I would consider a Excursion but they where out of my price range.