I have an 05 5.3 354k miles (original motor) and I’m having what I think is an ecm issue, but I want to be sure. A few months ago it started saying “engine overheated” or “engine coolant hot” and the temp needle on the dash would rapidly go up and down. Another thing it does, but only when you drive the truck cold is that around 45 mph when it says “engine overheated” and the needle goes up, the truck will do a shudder. I’m thinking it may be a bad torque converter. I read up that it goes into an engine protective mode that reduces the power when it’s overheated. I didn’t do a scan then, but I went ahead and changed the thermostat and coolant temp sensor. Then after driving for a few minutes it did it again. I decided to scan it and I had the codes P0327, P0449, P0117, and P1258, with the last two being new ones. From that I decided to change my coolant to make sure there wasn’t any air bubbles in it, but it didn’t work. I then put on a new temp sensor harness after the temp needle stopped working altogether (it works now), but it still says it’s overheating. The last thing I could think of is that it may be the ecm. If it is I haven’t decided if I would get mine refurbished, or get a new one and have the dealer program it for me.