Chevrolet Repair: 1999 Chevrolet Random Miss Fire, crank pulley, center bolt

Question
I have a 1999 Chevrolet Silverado 1500 2WD, 4.3L V6 vortex.  But I am getting a Random Misfire code out of the computer.  I have had the tank cleaned, changed the sending unit and pump, new fuel filter, Changed the Injection system (spider), new distributor, new cap, rotor, plugs, wires, etc the tune up.  But I am still having it hard to start and jumping after it has sat for awhile.  Any thoughts??  Thank You

Answer
Hi Brian,

Hook up a vacuum guage and watch the needle at idle.  Is it jumpy?  

Could indicate a worn timing chain.  To determine this, take off the dist. cap, and use a wrench at the crank pulley center bolt to turn the motor over slowly.  When the rotor starts to move, turn the crank pulley the other way.  If the crank pulley moves a lot before the rotor does, it would indicate a worn timing chain.  

Could be a valve issue, but unlikely.  

Vortec 4.3L is known for it's carbon build up inside.  It gets chunks in the EGR from time to time.

C J S