I just installed that kit (me, not a shop) 2 weeks ago. I have had no wiggling on or off the hwy.
wiggling happens when your bed moves up and down and your panhard/track bar is not in the correct position due to lowering. The panhard bar relocator that comes with that kit resolves that problem. The reason people have the butt wiggles is:
1) to much bouncing due to soft (cut stock) springs
2) soft shocks allowing excessive bouncing (buy the kit with the street performance shocks)
3) no panhard/trackbar relocator bracket
If you correctly install the 964sp with street performance shocks on a standard cab 09-12 Ram you shouldn't have any wiggling unless somehow your Ram or 964sp kit is built differently than mine (highly unlikely
)
As for the wheels being centered in the wheel well, that is really a matter of personal preference. A simple 2/4 drop doesn't shift the wheel off center enough to matter or be noticed by anyone. I asked a few people and they couldn't tell it was off center even after I told the it was. Like I said, personal preference. With the 964 kit they WILL be off center a little. To fix it requires you buy some more parts. I didn't do it so I will let someone else explain that. Here is a pic of my off center rear wheels.