The wallowing Lexus ride comes from the shocks, the springs are identical to the land cruiser of the same year, 80 series springs do change year to year though, look at the paint codes on the springs.
I just hauled an enclosed car hauler from GA to FL, weighed it on cat scales
front axle 2,460
rear axle 3,720
trailer axles combined 6,300.
GCVW 12,480
80 series is generally balanced front/rear difference is from tongue weight that takes weight off the front and puts it on the rear, I have airlift bags to help with the sag, even with the airbags weight balance on the trailer was touchy, weight few inches aft lowering tongue weight and the trailer swayed, few inches forward and the front end pointed to the sky, I need to get heavier springs.
This was mostly downhill but there were some rolling hills, even these gentle south Georgia hills it was doing 35 by the time I got to the top, max realistic speed on the flats was 49 any faster and the torque converter would hunt, after 51 or so it would lock, RPM would drop and it could not maintain speed, TC would unlock at 49MPH, RPM would increase, repeat over and over, millage was around 10 MPG, need more power.
Thanks to trailer brakes braking was the only thing that preformed well at least when it was dry, on the wet it got a bit sketchy.
Moral of the story 80 series can be pressed into service for occasional heavy towing but I would not want to do it often or for more than one day, it would be way too slow to cross the US, the rockies would be a real problem,
Diesel trucks are getting cheaper, IMO that is what you need to move vehicles cross country on a regular basis,