Originally Posted by viciousknid

The first thing to do is spray carb or brake cleaner at the intake on the sides and see if smoke comes out of the exhaust. that will indicate a leak or not.

Originally Posted by 02'Z71ONDUBZ'

It's not your throttle body. Those trucks have defective intake gaskets in many cases, if their the factory orange ones. The gasket material contracts in extreme cold temps, causing a vacuum leak. Once the engine warms up to operating temperature, in most cases, the heat will cause the gasket material to expand, in turn sealing off the intake leak. The service engine light is coming on because you have un-metered air entering your intake track causing multiple misfires. If your truck sounds like it has a huge cam in it at idle but runs like normal once the truck warms all the way up, and only does it on frigid mornings, you need to replace your intake gaskets. GM put out a service bulletin on this a few years ago.