2.3 Misfire

97, Did plugs, wires, fixed the lean code right after i bought the truck. It misses under a load, like shifting kinda early into 3rd, or putting the pedal down in 5th just to gain a little speed. No misfire codes have been made, but have had a manufacture emissions code come and go. something about a purge valve failure or related to a pressure change in the gas tank. I didnt think that would affect it but i dunno. code comes and goes, but still consistently has a miss while driving