1998 silveraldo engine missing

i have a 1998 silveraldo 350 c.i. that the service engine light came on. i went by autozone and they checked the codes and found random miss, some kind of lean code, and another i can/t remember. the truck has 81000 miles on it. i replaced the plugs and it seemed to help a little but i really notice a miss in the engine at stop signs but not all the time does anyone have any ideas with the spotty info i have given.