Yep, Google still works:
Top Pickup Trucks for Towing - 2005 Pickup Trucks - Cars.com
It looks like the Colorado is rated to 4K so you are pushing the envelope. An experienced tow driver on flat ground with the trailer properly loaded should be ok. A green driver with a tail heavy load might put it on the roof. I used to tow a 4000 lb boat behind a Toyota 4Runner and it worked well even over mountain passes but you had to stay vigilant. I never wanted to let the tail wag the dog so it was not a relaxed highway cruise.