help with site that xplains how to read codes

Hi.. was wondering if anyone has info on reading codes for a 1988 K-1500,

350ci or a site that xplains how to Truck,,runs fine then , as if running out of gas,, lack of power, engine light comes on , a few mins later of reduced power , it comes out of it.... engine light goes out,,( but seems damp when it happens which gets me into the electrical mode, replaced plugs & wires, so far,, anyway any help would be appreciated,, thanks snipped-for-privacy@gmail.com