You may have all your basic tuneup items to look at but, there are also emission related items to look into. Did your truck come with A.I.R. (air injection reaction system)? This includes your smog pump, air injection hoses which pushes fresh air into the hot exhaust through the exhaust manifold. What this system does is reduces HC's(Hydrocorbons). Your truck was originally equipped with the E.G.R.(exhaust gas recirculation system) What this system does is recirculate a portion of your exhaust gasses back through your intake into each cylinder's combustion chamber. What this does is reduces NOX(oxides of nitrogen).
Basically, HC's and NOX mix together to produce smog. The E.G.R. and A.I.R. systems are two of the main components of a gasoline's emissions system that are going to play the biggest role in your truck passing a smog test provides that your engine is in good health and your tune up is good.