Headlights and Interior lights flicker?

I take it the screw you are talking about is the one from GM bulletin #01-06-03-005. I suspect, since i've done a lot of GM 3.4L and 3.8L lower intake manifolds, that someone left a ground off somewhere or the charge wire at the alternator is not properly making contact. Another issue can be the battery connections as well - make sure those are tight. Also, not sure if you had your intake re-seal done at the dealer, but in April of this year, a revised intake manifold bolt torque was issued.

Hi, Yes that's the screw that was replaced. I will try to take it back to the place that did it. I will let them check it out, and will tell them to check what you told me. I had it done at a independant shop. I will also tell them about the bolt torque. Thank you so much for your kind help, I really appreciate it. Thanks!

Ok, took it to the place where the gasket was installed, they checked all the grounds, headlights, brake lights, battery cables, and they said everything was fine. I also bought a new Diehard battery and it still does the same thing. I also tried yeaterday, with the engine off, headlights on, and when i stepped on the brakes, headlights dimmed a little and then went back to normal. I had the re-seal done at a independent shop, they were aware of the torque issue. Do you have any other ideas what could be wrong? Thanks.