[sourdough]

You have a 2001 truck. At 21 years old I would look at the shocks and springs. Fatigue at that age would be normal for the springs and depending on how hard the life has been they could be damaged. Shocks should be new or almost new pulling that trailer. You didn't say what the payload on the truck is; do you know? That would give an idea if you had hd springs or the lighter ones.

With a 1/2 ton pulling a 65xxlb. trailer you need stiffer rear tires than OE. What are on there now? You want LT tires to minimize the squishy/wiggly feel of OE P rated tires.

I've not used the inside spring bump stops and wouldn't if they are just rubber pads. When the truck hits them they don't compress much and will jar the truck all the time. Air bags work well; I've used the AirLift 1000 bags and they worked on my 1/2 ton. Much more flexible than hard rubber bump stops. There are other options as well. There are Timbren rubber shock/springs that are progressive in nature as I recall. There's also Sumo Springs that are a progressive rubber compound that work well. There are a couple of different models of them. Maybe 10 years ago the AirLift 1000 was about $99 and easy to install inside my rear springs (Ram). I've decided if I do some sort of spring support again I'm going to give the Sumo springs a whirl...BUT, before you do any of those things make absolutely sure the shocks, springs and tires are in excellent shape.