1500 leaf pack (6200 GVWR) is 3 + overload. 1500 HD pack (6600 GVWR) is 4 + OL. 2500 LD (7200 GVWR 6 lug) is 4 + OL but I hear this OL is stiffer than the 1500 HD. 2500 HD (8600 GVWR 8 lug) is 5 + OL. 3500 SRW I'm unsure of, but they do have 9200 GVWR. My dually (10,000 GVWR) has a 6 leaf pack with only a lower overload which I thought was weird because the frame has the horns for the upper overloads. Then I just saw a dually in the boneyard with a 5 leaf pack and upper/lower overloads same 10k GVWR. That's what I know to exist out there. My half ton has the 7200 GVWR springs out back and it raised the truck an inch or so and made towing and hauling a lot better.