sounds like the regulater to me too because it misfires a little on start up. reg. was only about $50 when I checked on it yesterday.Also what are you calling the upper plenum on this is it the black plastic part where the throttle body bolts down just above the aluminum intake or above the throttle body where the air comes in, and how long does it usally take to do a regulator?
thanks again for your help Ive had a diesel for a long time and have never had this type of system on any of my trucks.

Yes, the upper plenum is the black plastic part. It is held down by a bunch of 10mm bolts. remove the fuel line and the big black injector harness connector(1 tab on each side) and its pretty self explanitory from there. Make sure you lube up the rubber seals when going back together it will make it easier to slide back on. You will understand once the upper plenum is removed

I bought a repair manual today and i see what your talking about now. It looks like you have to take alot apart to do it, will I need any new gaskets for the upper plenum to lower connection? Thanks agian!

The gaskets are reusable but a new set would be a good idea. The gaskets come in a kit through gm. Its packaged in a big white envelope. Just ask for upper plenum gasket
set.

the verdict is in! Checked the fuel pressure the way l82ofast said and it was the pump. New pump in, problem is fixed and it starts perfect now! Pump was only $135 and $8 for the strainer and it was an AC delco part. Thanks agian for the help guys it is much appreciated.

Good fix, and good price on the part.

I have pretty much the same problem with my truck, how hard is it to put a fuel pump in? I really am hoping it is the regulator though.

not bad depending on where you have to work on it and how rusty it is underneath there my truck is like brand new underneath and I have a lift so it only took a couple hours.