I have a 2008 4.0L V6. Recently the heat has been acting weird. I let the engine warm up, start to drive and the heat is fine, until I stop at a stop sign or red light and then it starts to blow cold air out (on any setting, but it's usually on feet and defrost), then when I start to move again, hot air returns after about 30 seconds or so. Usually when I warm up my truck, I let it run for 5-10 minutes then hot air will blow out, but now it doesn't really blow out any hot air until I'm moving. Then after about 10-15 minutes of driving it is fine and will still blow out hot air while stopped and other times not. Before it used to heat up in a matter of minutes, now it takes longer and longer to blow warm air. I miss being able to brag about how fast my truck heats up lol. Engine is running at normal temperature at all times as well. Any help/suggestions on what this issue might be would be greatly appreciated. I have read through here and other forums for any light on my situation and have not seen anything similar yet. Side note: Earlier this year in the summer. One morning I started the truck, then out of now where a loud hissing noise and mist started coming from the engine bay/under the engine. It sounded like when my buddy busted my A/C system hose fitting while putting on my steering extension for the body lift (that entire system was replaced). But it wasn't green colored like the A/C air was so I had no idea what it is. By the time I hopped out and opened the hood it stopped so I was unable to pinpoint the location of the leak. I have never had any issues after that with A/C or heat (that I'm aware of) so I'm not sure if this is what is causing my heating problems.