Greetings,
is there any tips does/ dont's when replacing intake manifold gaskets have I should know? Should I stick with A.C DELCO or does it matter? Should I use ultra gray silicone in the corners?
any help or info is very welcomed.

 

I would recommend Felpro gaskets. I've done the upper intake manifold gaskets on a Sonoma and a Blazer (both 2nd gens). Not the most fun job, but not the worst either. Don't try to do this job with the hood attached....take the whole thing off. Distributor has to come out, so be prepared for the re-install procedure. And take a bunch of pictures before and during...it's amazing how much I can forget about what goes where.

 

You will want the Fel-Pro gasket kit that has the metal carrier for the gaskets. You also might as well replace the valve-cover gaskets while you are at it. Go to felpro.com to find the part number.

This link shows a very good write-up that I followed, supplemented by my GM manual.
How To Replace Intake Manifold Gaskets On A GMC Jimmy 4.3 Liter V6 To Fix A Coolant Leak - GM Truck Engine Repairs

There are three things I wish I had done differently:
1) read more carefully the part in the above instructions about the hidden bolts that hold the AC/PS bracket in place
2) use a high-quality black RTV sealant instead of the one that came with the Fel-Pro kit.
3) use 4 of the old LIM bolts with their heads cut off as guide pins for lowering the LIM down in place.

You will spend a lot of time removing parts to get at the LIM gaskets.