I would be careful putting old (Pontiac Fiero) technology alarms on new vehicles with computers. The Body Control Module runs everything non-engine related on the Colorado and it could be damaged by splicing in the old alarm system. My truck came factory stock with an alarm, perhaps the BCM in your truck could be reprogrammed to allow the alarm to operate.
Maybe someone with more knowledge will check in.
2007 Colorado, Pace Blue, regular cab, 3.7, auto, ZQ8 , 2LT , 3.73, G80, tow package
Pace Edwards Jack Rabbit bed cover
Catch-All Xtreme Floor Guards
ZQ8 tailgate decal
Factory foglights added