The guys that are backing off these engines at 1250 degrees must either live where it is pretty flat or they think these trucks are dogs. I can hit what would be that back out point, empty on my comute home, going with the flow of traffic. Although I gain almost 5000 ft in elevation during my commute home from work, I usually don't worry too much about my EGTs unless I am really weighted down and then I am post turbo up into 1100 degrees sometime for minutes at a time with my 01.
One other quick thing is I saw a post with a link to the Cummins powerspec site and went and looked there. Here is a quote regarding the ISB Engine Protection system. The key item is "intake manifold temperature"
The electronic control system monitors engine speed, oil pressure, coolant temperature, coolant level, fuel temperature, and intake manifold temperature for normal operating conditions. If the limits of normal operation are exceeded, the engine will trigger the red (stop), yellow (warning), or blue (maintenance) lamps, perform the appropriate speed or power de-rate, and log the appropriate fault code.
The way I read that is that they are monitoring the intake and if it is too hot they will derate or throw a code. I didn't think it was doing that, correct me if I am wrong.
---Doug