So I bought a 6.9 off of Craigslist last night drove it home for about an hour and immediately started overheating to L on the dummy gauge, Dash gauge. The truck never actually went to full red line and showed no signs of steam or smoke so I continue to drive it home. I got it home that night and as I was pulling into the neighborhood it started to lose idle and lose power under acceleration and start throwing out a lot of Blue Smoke. i parked it for 10 mins started it back up and it ran fine for 5 minutes enough to get me all the way home but pulling in to the drive it started idling horribly and cutting out under load. I floor it and it jerks and stumbles to accelerate and when I lift off it blows a lot of blue smoke. I parked it started at the next morning started fine runs great for about 20 minutes until it heats up and then starts chugging losing power and rough and won't idle. Thinking I fried the head gasket or did some internal damage through overheating it, today I went and put a new mechanical gauge on the side of the block. To my surprise as the truck supposedly overheated on the dummy gauge and the erratic idle began to ensue the new mechanical Bosch temp gauge read 190 degrees. Apparently the truck isn't overheating. The previous owner put a brand new radiator and thermostat in it, and the water pump looks a few years old. I put a brand new Motorcraft thermostat in it today as well before I actually got a temperature gauge and realized it wasn't overheating. So now it runs incredibly rough barely idles unless I give it gas and when I give it gas it is billowing massive amounts of blue and almost looks like white smoke to me. I'm really hoping it's not a head gasket does this sound like one? I'm going to start it tomorrow morning and see what happens. I'm starting a now believe it might be injectors not working properly once they get to temperature. Is this a possibility? How about maybe just a malfunctioning lift pump. It almost feels like fuel pressure loss to me. The cutting out and loss of power under load. But why would that only begin to happen 15-20 minutes after driving it when it is heated up. From what I understand the truck has been sitting for a while and was only used to gather firewood by the previous owner and then it would sit all winter. Thanks!