Oat's has an '07 and Bear has an '04. Different setup. You can't say adding a RSB to an '04 is gonna help an '07.
Oat's, your 07 Z71 already has a rear sway bar. It looks pretty beefy judging by looking at mine. I think you'd be throwing money away replacing it with a new one.
The center of gravity on the '07 Z71 may be higher than your '05.
These 4WD (I assume yours is 4WD) Z71's are big beasts. You can't expect it to be "nimble". The fact that you feel your '05 was more nimble is probably due to weight, CG, tires, etc. I'm sure these '07's gotta weigh more than the '05's. More goodies....