It's a 2000 silverado 5.3l recently bought in September of 2012. When I originally bought it nothing was wrong with it, only when it shifted around 60 mph it was a little rough.

As it started to get colder around 30-40 degrees the rpms at idle started to go up and down between 500 and 2000 rpms and almost die at some points, then after a while of running about five minutes the rpms would settle between 500 and 1000.

It continues to get worse to the point that it almost died this morning. I noticed a high pitch whine coming from the bed of my truck area, maybe the fuel lines coming from the fuel tank? Not sure.

I bought an idle air control valve and put it in my truck. It made the rpms continue to go up to around 3000 rpms and wouldn't go down, so I put the old iac valve back in and still continues with the rpm issue.

I ran codes with my scanner and p0300 and some other codes popped up too, like too lean on left bank and right. I thought maybe the egr valve, o2 sensors, or intake gaskets.
I cleaned the maf sensor and throttle body plate, no change.
I did a quick look to see if I could find a vacuum leak and can't find anything. The only thing I didn't check while checking for vacuum leaks is I didn't take the cover off of the throttle body and look,yet..also have not changed fuel filter since I bought the truck. Any helpful suggestions are appreciated.
Thank you,
Steve