RE: Any 2009 manuals here yet?
CAGS/Skip-Shift is aimed at keeping you out of the lower gears and forcing you into the higher gears to get better mileage quicker.
If you're accelerating very slowly with low RPMs, the skip-shift feature will entirely block the gates to gears #2 and #3 via a solenoid. This means when you want to shift out of 1st, your ONLY option is to jump all the way to 4th gear. You *will not* be able to shift into 2nd or 3rd as in you physically couldn't move the stick there, it's physically locked out from you. This is done as a "cheat" to get a better MPG rating and thus less gas guzzler tax.
If you're accelerating a bit aggressively then the skip-shift isn't enforced and you can shift from/to anywhere you want.
So basically skip-shift toggles whether or not 2nd and 3rd are locked out from being used.