2001 5.3 running very rough, p0300

[Awesomeness]

I have a 2001 silverado with the 5.3. It has about 153,000 miles and I have been having an issue that I haven't been able to track down. At idle it has a miss at idle, whether it is cold or warm. My knowledge says it is a vacuum leak somewhere that I cant find. There is no miss at any other rpm than idle. Recently as it has been getting colder (sub-30 degrees F) when I first start the pickup it shakes violently at idle, but after it warms up for about 30 seconds it runs as normal. Today when I started it and was warming it up my SES light started blinking, even though it was idling as normal. I shut the truck off because I knew that meant a multiple misfire code. I tried to start the pickup and it would not start. I plugged in my code reader, and I found the code P0300, or multiple misfire. I cleared the code and it started up and ran just as normal, with no issues. I drove it around 30 miles, shutting off an turning it back on numerous times to try and duplicate the issue but the code never came back. I have checked the intake gasket, which seems to be very intact. Where should I look next? Thanks for the help in advance.