1250 Degrees is the temperature at which Aluminum melt. The heads, pistons and other parts in the engine are aluminum, or an aluminum alloy. If you keep the ETG's above 1250 degrees to long, you and start to deform, or melt parts. I know that even going back to the old IDI's they say do not go above 1200....... Also as Dave said.... you can exceede this for short bursts..... just a few seconds and then you need to back out of it an let it cool down..... how long does you 06 stay at 1350, what, if any mods have you done to the truck. I would think that if it was BONE STOCK, that it would never reach those temperatures in normal usage (towing, driving, etc) since Ford would program the truck to not run that hot for warrenty purposes... They would not let it keep fueling, or boosting to that level since they would not want to cause a warrrenty repair......... If the truck has been modified, or has some other issue, it may go that high, however, just because it will do that high, doesn't mean that it is ok to do so.....