Quick "jabbing" on brake and quick start??

[shooter]

When hit the brakes hard and/or quick i feel this quick jab. Sometimes if I get on it from a dead stop I feel a similar jab/snap. This makes me think its the chain is starting to stretch in the transfer case.

While on a lift, I can imitate this "jab" by grabbing the rotor and trying to rotate it abruptly each way. Also, if spin the front wheel, the rear doesn't spin right away anymore. Slight delay
Any ideas on what might be the cause of this?

I have a: '02 4.4i SPG, h&r lowering kit w/ rear air susp., 82k miles

BTW i'm doing the lower control arms and sway bar links this weekend if that would have anything to do with it.