Chevrolet Repair: motor misses when warm, oxygen sensors, cat jimmy

Question
i have a 98 chevy truck with a vortex 5.7,after driving for about 10 miles it starts to miss and ping.at first it showed converters were bad,i changed them.it still did it,i changed dist,plugs,wires,ingintion coil&mod.ive checked the egr valve it has no carbon in it.ive pulled the dist. twice to make sure its timed,still does it.its not showing any codes other than misfire on all 8 cyl.please help,thanks

Answer
Sounds like a bad number 8 injector, especially if the converters went bad, also what are the values of the oxygen sensors?  Are they reading right when it gets hot?  should fluctuate between 100mv and 900mv and not stay steady.  If the miss is on number 8 look at the bank two sensors, most likely pre cat
Jimmy