Anybody experienced this?

So my 98 chevy with a 5.7 has a part throttle miss that comes and goes. It's usually worse in the mornings especially if its cool and very humid outside. I had it at he dealer over the summer and they replaced an injector and the upper part of the manifold cause it was cracked ( plasic crap) that helped alot but it still does it. This morning it was bad and even popped through the exaust a few times. If you give it alot of throttle it doesn't do it but when you back off or just drive it normal it misses. Being intermittent makes me think its a sensor but it does not throw a code. The popping through the exaust makes me think somethings retarding the timing to much. Anybody experienced this? Sensors are to expensive to just start buying em hit and miss. Any body got any idea's? Thanks guys.

I WAS TOLD ON MINE(99 BURBAN) SAME MOTOR AS YOURS !
THERES A MAIN INJECTOR OR FUEL PRESSURE REGULATER UNDER THE INTAKE THAT SOME TIMES LEAKS(LEAKS FUEL WHEN ITS COLD OR SLOW DRIPS WHEN ITS NOT RUNNING) AND ON COLD MORNING STARTS IT MAKES THE MOTOR MISS FIRE, OVER LOADS WITH FUEL BUT DOESNT FLOOD IT! , WHEN MINE DOES IT IT FEELS LIKE ITS RUNNING ON 4CYLINDERS, AND HAS NO POWER, AFTER IT WARMS UP IT RUNS FINE ! ONLY HAPPENS ON COLD MORNING STARTS AND NOT ALL THE TIME , YES IT SETS A CODE AS WELL , SHOWS UP AS LEFT BANK RUNNING LEAN !

I had a 98 GMC with the 4.3L v-6, essentially the same motor, minus two cylinders, and it missed all of the damn time. Twice the mechanic found a short in the wiring harness to the computer. You may want to also look into cleaning your mass air flow sensor, and when is the last time that the fuel filter was changed? I would start with the fuel filter, it will only help the situation regardless if it is the main issue or not. My mechanic had a tool that he could hook to the truck that would also tell what cylinder was missing.

Thanks guys, fuel filter was changed in august. Mechanic said 5 and 7 were the injectors acting up. Flushed the whole system several times replace the one because he felt it was causing the other one to act up. It helped alot but it's started to get worse again. When it first started it would only miss above 2000 rpm but now it doesn't really matter what rpm. I thought about the MAF but hadn't looked to see if it was a MAF or MAP system. Didn't think MAF was as common anymore. I'll check that as well. I know I've had trouble on my old toyota back in the day with the MAF.

It's funny about chevy's, they will still run without the MAF sensor connected to the intake, but Puddin's toyota won't even start if the intake is slightly loose after the MAF sensor

cody do you know any gm master techs in the club....call him...he might be able to help

mine 96 4.3 does it all the time in the morning but if i let it sit for awhile and drive it, it doesnt do it anymore it sucks but i just jump in the guts of it and it clears up