Lots of people on here reporting using GX470s, GX460s, and V8 4Runners to tow 4,000-5,500# campers through the Rocky Mountains. I have a 4,000# (loaded) low-profile camper, have pulled it thousands of miles with my GX, and plan to pull it out west in a couple of years (after a 4.56 regear). I routinely tow it 70 mph around here on the highway and pull some very steep hills (10-15% grades) and have pulled it as far as 700 miles in a single day.
FWIW, we passed on a 4-5,000# non-collapsible camper specifically because I wouldn't be comfortable pulling that out west with my GX, although other people report good experiences pulling similar campers with theirs.
Assuming the hybrid works out OK, the LC250 should (at least on paper) be a better tow vehicle due to better low-end torque coupled with a similar overall size to the 120/150 platform vehicles.