Somebody was pulling you leg when they told you got 4 yards of topsoil in your truck my old 88 F-Superduty with a 12x7.6 foot box and 2 foot sides could carry 3.5 yards. I put 4 yards on the truck the soil was fairly moist but I figured I had close to 8500-9000lbs on the truck. If you haul mulch thats heeped above the box it must be tarped if the topsoil is really dry it must be tarped legally every load is supposed tobe tarped from gravel to topsoil. I have carried close to 3 yards of drain rock that was damn heavy the load scaled out at 9100lbs pushed the gvw of the truck to 17,300 A landscaper friend of mine he isn't used to trucking he didn't realize the the weights of gravel the pit dumped 3.3-4 yards of 3/8s minus into his Chevy 1 ton. I told him he had close to 5 ton on the truck he somebody told him that he could pack 3 yards so thats what the loader operator gave him I deal with the pit alot and know all the guys that work there I gave them s--- for overloading my buddies truck told him he is a novice in trucking. I told them "you guys should know better"