Coming up here soon I'll be tackling my 2006 Grand Prix GT 3800 III Lower Intake Manifold job..

Anybody have any suggestions of things I could or should replace while I have all of that off off the motor?
I thought about dropping in new LS7 lifters, but mine are pretty quiet....
I am at 148k miles

Is the LIM gasket leaking?

While you're in there, replace anything that is a gasket and anything that is a sensor and hasn't been replaced recently.

I am pretty sure it is leaking, not badly yet though.
I flushed out my radiator a while back, and drove around for a few months, then I noticed the coolant in my overflow was getting darker.
Being a 2006 and already having the aluminum coolant elbows, I figured the gaskets must be aluminum, but oil is deff getting into my coolant.
I plan to change the SC gasket, LIM gasket, both valve covers, plugs and wires...
I am pretty sure I replaced my water-pump with the aluminum framed gasket 2 years ago, and then did not drive it for 2 years, lol
I replaced the tensioner assembly already..

I know the crank and cam sensor will be easier to do, not sure if I should go ahead and do those or not, my car is almost at 150k and I am betting they are original.

I am not rich, but have enough money to replace a few things that could go bad in the future, things that would be easier to do while I have it all torn down..

I think I will need a new rack in the future, but that is for another thread...

Actually with the crank being so low I can do that if it ever starts to fail so I am not going to bother with that.
Plus my luck I'd have to have the CASE learn done..

I really want to better headers on because sooner or later I want to put a beefier exhaust system on, my thoughts are I want to maybe add a few mods in the future to add HP, but first and foremost I want the car to be able to breathe as good as possible.

While doing the LIM gasket job it would be a good time to do headers, but could I get better headers that will fit my current exhaust..
Only thing is I do not know a lot about exhaust systems, all I know is I'd love to step it up to a 3" setup, and get the best one I can, I don't think I have to worry about emissions tests here....
I could start another thread dedicated to this question, but this thread is for suggestions on what I can do that will be made easier while I already have the LIM removed...

Then again if I go from 2.5" to 3' I am sure the car wont run as optimal as possible, so I should probably not go bigger until I can mod enough to increase the output...
Are there any 2.5" setups that would sound beefier, and add a few more HP?

Ah okay. Seems like you're on the right track there. If it were me, I'd do the crank and cam sensors while in there. Then you'll likely never have to do it later.

3" is too big in my opinion . . . unless you plan on getting 600HP out of it, 3" won't really help you.

You might want to check out zzperformance and see what they have.

FWIW The exhaust is engineered to be near optimum for that engine. The only thing that happens from adding a larger exhaust is to lighten your pocketbook. Without pushing more air there'* no need to waste your money.

Makes sense, I and my wallet like that logic.. Thanks.