Bed Rail Height Issue

My brand new 2 month old Ram 3500 2wd CC LB with Cummins sits at 58" at tailgate straight from the factory. It also has the optional air assist rear suppension and I was just barely able to make it work under my 2018 Grand design 337RLS at 5 !/2" of bed rail clearance and a level RV. When I loaded 2400# of bagged concrete mix between the tail gate and the axle it only lowered the tail gate height by 2" after I pushed the alt. ride height button. Yes these trucks are tall. My old 25002wd was only 52" at the tail gate and the same 5th only lowered the height by 2" loaded for a trip and it had no bags.