holley allison

I have a 03 ram 3500 I have hauled some pretty heavy loads but have not overloaded truck, My problem is I have a low speed shudder coming from the rear of truck below 15 mph I have tried coasting to a stop and it is still there, any ideas

I have a 03 ram 3500 I haul some pretty good loads but not overloaded, I am having a problem with low speed shutter from rear end around 20 mph to stop, does not matter if i am on the brakes, I am thinking my rear leaf springs are bad any suggetions