Troubleshoot *this*, She kicks like a mule Options

[qatar11]

So about 3 hours into our second run after the brake leak (more on that later) we noticed a hesitation or a feeling of a misfire around the 6K mark (7AFE 5spd) as the driving session turned into a 4 and 5 hour run this feeling feel to the 5K mark and into the 4K mark. At the end of the race (call it 15 straight hours of driving) the car was limping around the track in 5th gear chewing up laps - nothing above 3K really without getting the hesitation.... we think its heat related and we think in between driver changes, it gets better briefly - so we think its something that does not retain heat like cast iron.... so.... what do you think it is?