CAGS, for Computer-Aided Gear Selection, is a misnomer. Given certain parameters such as gear selection (only happens in 1st), speed, throttle position, and engine temperature, CAGS causes 2nd and 3rd gear to be locked out, forcing a 1st to 4th upshift. The theory is that by lowering RPMs, GM is cutting fuel consumption and, probably, noise pollution. I usually stayed in 1st longer to avoid it -- so much for that theory.
I say it is a misnomer because it acts more like Computer-Thwarted Gear Selection. For example, I know I'm about to go around a tight corner that I'll want to accelerate through. Unfortunately, the PCM decides it wants to be is fourth so you either over-rev or bog like crazy.
Anyhow, it didn't take long for this game to get really old so I pulled the connection to the solenoid on the transmission and taped it off. People will be happy to sell you a resistor kit for $30 or more, but my solution has been working fine for almost 20 kilomiles. Unfortunately for those with '96+ cars complying with the dreaded OBD-II, you'll get a ``Service Engine Soon'' light if you tape-off or have the wrong load at the solenoid connection.