need help 2002 g-2500 5.7
 

fresh motor not even out the door yet. Problem is misfire monitor shows no 2 cyl missing badly. road test. shows check eng light blinking then not, then blinking again sometimes 9 times sometimes 30 times. new dis, new wires, shanged plug to no 4, nochange, changed wire to no4 no change.
changed dis cap no change. mil light does not set a code always, but misfire once in awhile. and can watch no 2 on monitor misfire regurally
need help to pin it

I have had a similar problem with an 03
anything above 55mph would result in a flashing check engine light. I could monitor the misfires on my computer and there were tow misfires on 3 and 6 I think with random jumps on all or random cylinders. I tested and tried everything and ended up giving it to the dealer and their expensive computer. They ended up performing a crankshaft variation learn procedure and that solved the problem. I even swapped out a crankshaft position sensor with another truck and no go.
Good luck!