1995 silverado 5.7 missing

I have a 1995 silverado 5.7 L throttle body. My gas milage is terrible average about 12 mpg. It has a slight miss while sitting still. Also if I am going about 50 mph or so and my rpms hit around 1700 it really starts to feel like its missing like heck. What do I need to check for?????????? I am gonna change the distributor cap today. The check engine light is not on!!!!!!!!!!

hmm... my only guesses would be with the ignition system. Distributor cap, rotar, plugs and wires?