I need some insight on my truck misfire problem

I have a 2003 chevy silverado 1500 4x4 5.3L flex fuel truck
with a Z in the VIN.  It is throwing a p0300 random misfire
code. From a cold start I can take off and drive without a
problem as long as I drive without stopping. now when I get
in stop and go traffic and sit for to long (say at a stop light) it
will start to idle rough.  Then when I take off it barely wants
to pick up speed I will push the gas pedal halfway down the
check engine light starts flashing and still barely going
anywhere. but when I smash  the gas pedal to the floor it
runs rough for a second then its like the whole engine kicks
back in. and also from a cold start if I don't get stopped in
traffic it will run good to the place I'm going but once I get
there and shut it off then come right back out and start the
truck it starts running rough again and check engine light will
flash when I'm taking off. But if I shut it off at a stop light real
quick and start it again and take off as long as I don't get
stopped for to long it runs fine.  When its running rough you
can smell gas too.  I have replaced the intake gasket with the
oem one (kind of pricey $80). replaced spark plugs and wires
with a/c Delco ones.  All new coil packs accel super coils.  
Replaced fuel filter.  New converters  on the exaust.   When
its running rough it makes kinda like a Cherping sound not a
knocking sound but like a bird Cherping.  When it is running
fine you don't hear the Cherping and the engine runs perfect
you can barely tell the truck is running it idles so smooth.  
Could it be the TAC module or the ECM or the MAF sensor or
fuel injectors.   Please does anyone have any suggestions.