A leaky carb can definitely create a rich condition. The carbs on the trucks are pretty bad. If you want to keep it bone stock, rebuild it. I don't know what the emissions rules are but another option is replacing it with a Weber and dial the jetting in for emissions. But that would remove the thermostatic air cleaner, the EGR and the pulse air pump ehich could make your emissions even worse. I don't know the legality of that. The simplest and probably safest option is rebuilding it. $270 is a lot but it's less than a Weber. Get a warranty on the rebuild if you can.