I recently took the rear leaf springs off my 49 1/2 ton (swapping rear end as part of putting in an open drive shaft/t-5 conversion).
Anyway, I put the two leaf springs side by side and the passenger side spring ends were a good inch lower the other side (passenger side had "de-arched" more over time). That's enough to cause the bed to sag an inch on the passenger side, all other factors being equal.