Trucks a '76 620 with 720 4x4 leafs, stock shackles, and 2'' blocks.
I've been getting this weird problem ever since putting in 2'' lowering blocks on my 620. Every once in a while when I take my foot of the gas to coast or slow down, I've noticed the truck pulls from left to right rather hard (but most of the time rather mild.) It feels almost as if the rear diff is just floating around under the truck. I checked everything and it seems to be pretty tight, so I'm not sure why I'd be getting this sensation.
Things I've noticed in particular:
It doesn't pull directly to any side in particular.
If I jump back on the gas, it straightens out.
It LITERALLY feels like the rear of the truck is floating around.
It's very inconsistent and seems to get worse after hitting a bump HARD.
I know my passenger rear brake is dragging very lightly (trying to figure that out still) but I don't feel that's related since it doesn't just pull to the right.