I too am faced with the leaking intake manifold on a 99 gmc suburban.
I think mine is leaking from the front just below and to the right of
the t-stat housing, unfortunately I pretty sure it the intake gasket
and not the T-stat, dry as a bone up there. The leak has gotten a bit
worse, brought it to a mechanic who replaced the water pump which I'm
sure had failed, fluid everywhere....
I am now at the point of deciding wether to fix it or dump it. I've
got ~120k on it now and it's had the fuel pump done, decent tires.

One of the existing problems is during the warmer months it idles rough and sometimes even stalls at
idle when in gear but at a stop, put it in park and it runs smooth. I
wonder if this could be related to the leaking manifold gasket, if
it's leaking interally too. The only other thin I can figure might be
causing problems is the remote start, astroflex/start mv801, the
install was obviously a butcher job, as I've traced the wires, one went
to the coil and was just twited on an taped, no solder... Recently there are times when it just won't start, if I disconnect the battery and reconnect it starts right up, I do believe this is related to the darn autostart and plan on removing that, at least while troubleshooting.

I also see that the temp doesn't get over 130 what's the normal t-stat
open temp 195? During the cold weather it seems fine, other than having to add coolant. I'd really like to get a handle on the stalling before tackling the intake manifold.

1999 5.7L k1500

How is the fuel mileage? The stalling problem may be related to an overall leak in the intake gasket (more than just coolant) or something in the upper intake (like injectors or the regulator) that you will be uncoverig as the project progresses.

A cooling system pressure test should provide clues about where the leakage is occurring.

just to share in your missery I have just had the h20 pump and lower intake manifold gasket replaced and its still leaking!! 80k miles too soon for this to happen on a 99 sub k1500.

Sorry to hear of your

I did the intake manifold gasket, split the manifold and did the de-carb, threw in a new fuel pressure regulator while I had it open. Broke the water inlet quick disconnect tube while trying to wrench it off. From what I've read here it was a typical repair. There sure is a lot of gear on the engine, but at least it's done.

The engine definately runs smoother but still does it's thing when it's been driven on the highway for a while. EGR? I'll make a separate post about that.

Blue Bowtie - Thanks for your input, I had lost track of this post. I don't know how to test the injectors and did not disassemble the csfi, just put a new regulator on and got the poppets back in the correct port.