OK, I'm looking at your last pictures. The 4" lowering blocks will add a lot of leverage to the rear axle on the springs under acceleration, and when stopping. I believe this could create a lot of wheel hop in both conditions. The blocks may amplify the rear end steer as well (something I didn't think about).

How much ground clearance do you have for the frame as it currently sits? Have you taken into account how much the chassis might lower with all the weight on it? Gene