I had my car up on stands today and noticed the TA had moved out and then back in at one point. (slid back towards the rear end out of the C-clamp about 1/4 of an inch, its back in its normal position now) I know this because I sprayed some white grease around the area before and there was a notable mark in the greese where the ta slid out of the c-clamp a little then moved back. Is this movement normal or do I need to tighten my c-clamp?

 

That's the whole point of GM designing it with a sliding bushing. If it didn't need to move back on forth there wouldn't be a sliding bushing there, it could be just a round bushing like a control arm.
The control arms set the position of the axle fore and aft but they travel thru an arc as the rear goes up or down. This arc along with drive and braking forces makes the TA move forward and rearward slightly.

 

The torque arm will slide a tiny bit when the suspension is moving up and down. Just make sure things are tight.