croady - Right. 4-flat connector and 1-1/4" receiver is NOT the factory HD towing package. You have 3500 lbs, Class 2 towing capability, regardless of engine.
Like someone said, if you have the V8, you can simply upgrade your receiver to the Class III/IV unit, and have a trans cooler added, and you will be set for full tow rating somewhere around 7000-7300 lbs.
If you have the V6, you are stuck at 3500 lbs MAX, unless you upgrade your rear axle.