Hi everyone. I am new here. I have an 2005 with a 4.0l manual tyranny. After the truck has warmed up the rpm's drop and come back up at idle. This continuously repeats itself. Also I noticed that there is some small holes in the side of my muffler and i can here the noise that corresponds to the rpm's there. Any chance this is related. One more issue is that I also have a k&n filter and the other day while checking it I noticed a crack in the airbox which I patched with duct tape for now. Thanks in advance for all your help.