I have a 1996 K1500 Pickup with 3.42 gears and I want to upgrade to a 3.73 or 4.10, but I don't know which one would be better?

I plan on installing a 3 inch lift with a 305/70/16 or a 315/75/16 tire.

Can anybody help me?

 

Best way is to call your local chevy dealership. give them the vin number and let them do all of the work. you can get axle ratios, whether or not you have a locking rear end and what axles you have.