it started a few days ago while driving home my truck felted as if it bogged out for a second and then rpms started jumpin all over the place and then truck died it wouldnt start up after that. i towed it home and have replaced fuel pump and filter new plugs and wires new cam position sensor and crank sensor new cap and new plastic piece inside that as well as well as new ignition coil. the truck now starts up and dies sometimes and sometimes it idles fine at 600 rpms but then i go to drive it and it now does the rpms jumping all over and tries to die but if i keep givingh it gas it strugglers but will correct itself but not for long im at a loss as to whats wrong, is there anyone who can help me figure it out. i never had issues with it before except randomly very few times did it chug for a second while on cruise control at 70mph. is there a chance ive missed something? its the 4.3 vortec with 173k miles on it. its getting fuel and i have the fuel pressure tester it has the right pressure while running and off. even when in park it idles in right range but it just dies rpms only jump all over when im driving not in park. im gettin fuel and spark.

 

did you check A - Regulated pressure hold time, should hold above 55-60psi for 10 minutes at the schrader valve on the fuel rail. and B, have you verified you dont have any stored codes, intermitted short, etc. and C have you tried unhooking all vacuum operated accessories (4WD, HVAC) and capping the ports at the Vacuum junction, located where the Crankcase Vent valve hooks in on the drivers side of the upper intake manifold (the plastic bit)

To test - hook up gauge, turn key to ON, not CRANK, listen for the fuel pump to run its prime cycle (approximately 2 seconds), Turn key off, notate initial reading at prime cycle cutoff, have a 10 minute union break, and recheck reading, at no point should it go below 55PSI, and 60PSI is avg.

 

The rpm’s on my 2001 zr2 where going up and down, I was getting air into the intake, after Mass air flow sensor . Some vent hose wasn’t connected.