Hey guys i have a 2004 6.0 with 127000 miles on it. My issue is when the trucks is warmed up and im driving down the freeway or under lite load the heater/defroster blows warm. Then when i let off or am sitting at a stop or idling it starts blowing cool air like almost a/c cool. It pukes if i put too much coolant in it i think it suppose to be 1/4 below the min line. It doesnt really puke now im running stock file with afe intake and exhaust. I was running erics files but im almost certain my egr cooler and oil cooler are toast. So im trying to baby it tiil i can fix it all. My question is do you think its egr related or headgasket related. Or possibly heater core or thermostat? If i add coolant it doesnt do it as bad until it pukes. Thanks for any help and sorry for the long post.