I'm not sure about this statement. I have an 855s and fully loaded is north of 4k and I am tickled each time I load her on. System works perfect and when going down the road the ruck rides great. I couldn't be more happier with this setup.Do a bit of research before you choose the rear air option if using a truck camper. On a truck camper forum I frequent there were discussions a while ago of problems with the rear air if people load heavier campers in the bed of the truck. The rear air struggles to lift the camper, gives an error message. Not sure if it's true, but worth some research.
Scott