Paul,
We have about the same situation with respect to never having had a handling problem with our 2005 24 foot E450 Class C in stock configuration ... this includes a 7000 mile trip and a 9000 mile trip. One of the trips included a scorching Texas Panhandle in August and one of the trips included the mountains of Eastern Wyoming..
You might want to try a trip towing your Cherokee in Eastern Wyoming. On at least one major highway route there one can travel hours and hours up/down grades at continuous altitudes over 8000 feet at full highway speeds - if one's rig can handle it. We did it easily - however without towing - via the E450's aggressive rear differential ratio along with using sustained V10 RPMs above 4000.
FWIW we're planning another 7000+ mile trip starting late this summer, but probably will replace the stock Ford shocks before the trip.