I have a 2007 Pilgrim 39' 5th wheel (So there is no manufacturer to refer to nor any warranty to worry about) that comes in at 14.5K GVWR. I normally leave this camper at my site which is about 250 m...
How high is high? On a level surface measure the frame to ground in the front and rear. Post the results. Also check if your springs are sagging a bit after all these years. Maybe post some pictures. Otherwise you need to lift the trailer to match the new truck. Or forgetaboutit.