Can't say regarding the new truck. My truck is pretty much the same as your old truck and it squats 1 1/2" - 2" with a 2,000# pin attached. I hope that reference point helps. It sits empty with a little rake so the truck rides pretty much level when towing. I couldn't "upgrade" my truck as my trailer overhang is only 57". Nor, could I sell the trailer to someone with a newer truck. Probably will have to go as a combo when the time comes. It could be worse the, 4WD Ford F350 sits at 60 1/2".
It sounds like you haven't purchased the truck yet. When I was measuring bed rail height on trucks, I found the duallies sat about 2" lower. The Ram was at 57" but that was a few years ago.