Air filter was changed when I got the truck back in July from factory to a K&N, I have been thinking about this quite a bit and have invested in a factory repair manual, but I have compiled all of my symptoms in to this list Poor MPG, the rough idle, running rich/suited up plugs.
I was discussing this issue with a family member, we came to the conclusion that it may be in the fuel system somewhere what ever the issue, because I have no loss of power that I know of and a loss of power would point to an air restriction I think. There was one more item that I noticed while looking over the engine, there was what I think was a hissing coming from the driver side near the firewall. Any ideas?
To answer Psychologger it seems to happen after the trucks stops running through the cold loop, if the truck is warm it usually starts immediately and it will keep vibrating until I shut it off, although the vibration gets worse as the tank empties which boggles me. so a full tank will have less of a vibration but still very noticeable then when it gets to about half it will be at its worse. This seems to be the trend.