Engine idles rough and sounds like it wants to die?

I have a 98 Chevy Silverado K 1500 V8 5.7L it has started to idle rough not horribly but enough that you can tell. After being on the freeway and then coming to a stop when it sits for a few minutes at a light I have the feather the gas pedal to keep the truck started and to get going again smoothly ( it's an automatic) so I'm not really sure what's going on I know my way around an engine for things but not for something like this..