I have a 2002 silverado 4.8 4x4 125k miles
Problem is when its cold outside below 40 and i try to start it it wont stay running and rpms go from 1200 down to 400 then it dies
But after it gets to operating temp its fine? Im going to replace the battery friday because it needs it but i was thinking maybe intake gasket?
Any ideas? Plugs and wires are new
Bad battery wouldnt cause this would it?

I don't think that is a battery issue. If you had a bad battery it would barely turn over or it wouldn't at all.

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Try replacing the tps sensor its probably bad.  Look it up on google first check your symptoms and is it throwing any codes?

It throws a code once in awhile saying misfire but goes away after it warms up.
Spark plugs wires and coil packs have been tested

The reason i thought it was an intake gasket is about every 7 months i have to put coolant in it

Look into your intake manifold and check with a flashlight for oil there should be oil in there if the gasket is bad.  If that is the case and you take it somewhere VERIFY that they change the oil as well.  My dad had a shop change his and they didn't change the oil and it blew the engine cause the coolant seeped into the oil and threw a bearing.  I changed my intake gaskets in my truck and made sure I changed the oil and it is still running strong now it has 230,000 miles on her.  Also how does your oil look black, brown, milky?

Black

You probably have a blown intake manifold gasket.  If I were you I would look up how to repair it and do it myself.  You will save yourself quite a bit of money, around here mechanics are charging between 800 - 1200 dollars to do this job.  The gaskets themselves really aren't that expensive.  Other things your going to need are coolant and oil.  My suggestion is to drain all oil and coolant before you start if you decide you want to do this yourself.  Also before you start check out youtube see if you can find some videos of it being done that way you know what to expect.

Also check your oil sending unit which I believe is in the back of your engine and could be pushing oil into your intake manifold as well.  This should be easier to do as you just remove the plastic cover a few screws and you can remove it and replace it with a new unit.

Good luck let us know what you decide and how it turns out.

edit: Wait is your oil black or the inside of your intake I just reread your post and you didn't indicate which one.

Oil is black and local garage said they would do it for 325$ another wants 365$

That price isn't that bad.  Like I said earlier make sure they change the oil afterward.  Even if they say that it wasn't needed do it as a safeguard.

The only part of the cooling system that runs through the intake is through the throttlebody. otherwise the intake is dry, if you remove the throttle body from the intake you can remove and replace the intake gaskets without even touching the antifreeze level. hardest part of the whole job is unhooking the fuel lines. it requires a special tool. id spray some carb cleaner/brake kleen around the intake behind the throttlebody and against the heads to see if there is a vacume leak.(sounds like one)