H3 Alpha Trailer towing once again.......

OK I am going to show my ignorance on this..... What determines trailer towing capacity? Now before  you think I am a real idiot, I am sure torque and rear end gearing plays a major part. But why would an Avalanche with very similar specs (Listed Below) have such a higher towing capacity?????? Is it the frame? Wheelbase? What??? I am looking at a 4300lb dry weight trailer but just don't want to push it.....

                               Alpha               Avalanche
HP                         300@5200           320@5200         
Torque                   330@4400           340@4200
Rear End                    4.10                   4.10
Curb Weight               4851                  5729
Engine                       5.3L                   5.3L
Wheelbase                 111.9                  130

Towing Cap                6000                  8000

Weight of the vehicle...
 
Liability...
 
There are many factors
 
6000 or 8000 or 10000 usually has an asterik beside it that says when properly equipt'd
 
This isn't a bad article to read....
http://www.traveledlanetrailers.com/trailering101/trailering1d.htm

Thanks Muddydawg.... Great article....

One thing I forgot to ask was.....Does the Alpha have a trans cooler??????