Pretty much what BHolm said. If you are modded, especially if you have advanced injection timing, then the max sustained temp will be lower than a stock truck, at least in my opinion. I have heard of many stock trucks running 1400 deg on a regular basis without issue, but I have heard of a few guys advancing timing too much and trashing pistons/dropping valve seats at the same temps. For myself, I consider anything over 1300 deg continuous on a modded truck to be "no mans land".