Can I increase my towing capacity by changing the 3:73 gears to 4:10s

 

yes but unless you get it certified it wont increase you GVWR by DOT standards

 

In other words while the gear change physically changes the vehicles towing ability, legally it does not. As far as the state is concerned the CGVWR would still be the same. It could result in a citation in the event of an accident if it is found to be "overweight".

 

Would I have to have a gear change certified by a GM dealer or just documented

 

i know around here we have a certified spring shop that will cert a vehicle. but then you also have to up your registration and that "might" effect insurance if you tell them