rear suspension question

[gasmn1620]

in the interest of full disclosure the rear of my truck is lowered with the brackets that specialtyretail sells here..... now, on to the question. Since lowering it I had to cut off the bump stop bracket because I was sitting right on it. Now I have a few inches of suspension travel. When I press the accelerator something in the rear is shifting. The truck goes to the right and then when I let off it settles back straight.

I've been under it and everything is tight... u-bolts, leaf spring bolts (leafs have new bushings), probably needs new u-joints soon.

Could it be motor mounts? I don't think that would cause the shifting in the read end though.