I will notice two phenomena's when in regen, per the EGT. 1st is the standard temps will rise 200+ degrees (its hard to know when towing heavy) above @ 650*. 2nd is the Exhaust Brake will engage causing the EGT to rise when sitting at a idle. Now if I let it idle for 5 minutes, the EGT will drop below 500*, other wise it will rise when coming to a stop light. I'll see 650* when crusing at high RPM's @ 35MPH (I have the G56 manual trans), when I come to a stop my EB will engage and the EGT will rise as high as 850*.