Recommendation needed for first camper trailer

theoldwizard1 4 people will be in truck (2 adults 2 children). Not so much in the bed, its only 5' maybe 2 dogs and some gear. GVWR is 6k,the type of towing will be hills and mountains, some flats. No dirt bikes or quads. The bunks will be for my kids.
KD$UPL the standard Colorado is 7k towing, ZR2 is 5k

thank you both for your insight and wisdom!