First off, changing your rear end gears will not increase your truck's towing capacity or GVWR. Getting more aggressive gears can help you tow more effectively by adjusting your truck's rev range to keep your engine in a more optimal power band for towing, but your actual weight ratings and overall load capacity DO NOT change. Now, the Boss 302 manifold package will increase your truck's power output by a pretty significant margin, which again, will help improve performance while towing, but WILL NOT increase your truck's rated towing capacity or GVWR. The only upgrade that actually increases load capacity would be a set of Add-a-Leafs, which add roughly 950lbs of load handling ability.