does it stall at all while decelerating? i have the same problem with the sputtery-sort of rpm fluctuation. i replaced the plugs and i believe its an EGR malfunction. try running a code reader through it a few cycles.

 

Not sure about during deceleration.....but, I made an EGR block off plate and will be trying that out tomorrow and let you know what I find.

If the plate makes a difference then I will clean the EGR valve first before replacing it. It is worse not with no load, it actually drops almost 350 RPMs now.

 

No CEL lights doesn't mean there aren't any issues, just they haven't happened enough to light up the WALLET light - yet. Get it scanned.
Vacuum was ok, what about under the dist. cap? Rotor, cracks in the dist. case, fouling under the cap etc?
New engine may have an issue with the CKP - crankshaft position sensor, try a spacer & trust me you can use a rubber grommet as a spacer. The GM part # escapes me right now but up to 1/16" will still work.
Cold air intake? MAF - has it been cleaned? IAC - Idle Control Censor (I still don't know where that is)
Cleaned the throttle body? If it's sticky that may be the hessitation.

Just thoughts

 

Thanks for the input.....mine does not have CKP sensor...it is OBD 1.5 cap, rotor, plugs (delco rapidfire) and wires are new. And no MAF sensor either...IAC I do have.

 

Installed the block off plate and no change. Also cleaned the IAC, it was a little dirty but not much.

Hmmm.....so just for giggles double checked the timing again and it is spot on.....I know on our balancers ther are 2 timing marks....as I was checking the timing I thought I would see where the other mark was at in relation to the other....

I was under the truck and shooting the balancer and noticed that the second mark was a few degrees before the other (what looks to me) timing mark on the timing cover. Should the timing marks line up with each of their corrosponding marks or just the top one.

The truck starts great and idles ok.....

Oh, almost forgot.....I also held a napkin up to the exhaust at idle....now I know that if you have a sticking valve it will almost suck the napkin out of your hand.....well mine wll just suck it up quickly but, not much force....so, could I be looking at a possible sticking valve???? If so, is there any thing I could do short of pulling the heads???