1997 Z71 miss
 

truck misses in overdrive at speeds over 55mph idles fine runs strong under full power. coded radom cyl miss fire 5.7 was coded by GM tech at the shop and driving down the road. He suggested basic tune up plugs wires R button cap fuel filter which I have done He also to check the distributor gear for damage found none I have also run high end injector cleaner 3 times shell high test gas. The miss is radom for sure but only in od under almost no load any ideas would be appreciated