Seriously, something is bottoming out, may be driveshaft, or nose of the diff, but something is.
Lowering blocks WILL NOT make the car stiffer. Ever. They can't. All they do is move the differential further away from the springs. They don't effect the springs.
You're probably sitting on the bumps stops with the diff hitting the floor when you shift.
x2 on the bump stops. Suspension travel is reduced which tends to hit the rubber bump stop specially with a 2" drop. Suspension pop could just be a matter of re-tightening the u-bolts. Assuming you've got new shocks since that'll make a big difference on damping. Hope this helps.