Rough Idle on cold start

I have a 2001 silverado Z71 with the 5.3L with 60000 miles. I am having problems with it not wanting to stay running when you start it when the temperature gets in the 20's F. and it only does it if it has set for like 8 hours. When you start it in the morning it will idle up like it should then come down to around 800rpm and after 1-3 sec. the rpm will fall to 300 to 450rpm making the truck shake. Then it will rev up and catch back up to itself then do the same thing, sometimes it will even die. I got it to register the check engine light but after about a minute the light went off and I couldn't get the code from the machine at an Oreilly's. This only happens after the vehicle has set for long periods at a time and when it is cold. It is fine when the weather is warm. after you start it in the morning it is fine the rest of the day. The service center checked the vacuum system and it checks ok but I don't know what else it could be. I want to put remote start on it but I can't do that if I have to keep my foot on the gas in the colder mornings. You have any suggestions?
Thanks,
Travis

Could be the fuel presure reguator. They are known for causing problems like this. Also at 60,000 miles you should change your o2 sensors. Hope this helps.

If you want to know if its your fuel pressure regulator, just pop your hood and its on the drivers side of the fuel rail, pull the vacume linr off of it after you shut it off. If fuel comes out, thats your problem

If you want to know if its your fuel pressure regulator, just pop your hood and its on the drivers side of the fuel rail, pull the vacume linr off of it after you shut it off. If fuel comes out, thats your problem
If that does not work try the idel control valve, it lets your motor revup more when it is cold. So if that is bad it does not rev up all the way and wants to die.

I will try the fuel pressure regulator over the weekend and see about the idle control valve. What do you you think about the intake manifold gasket being cracked? I have heard that they sometimes can cause problems like this.