ISF overheating at the track?

Hey all,
I'm new to the ISF site, this is my first post, but have been following the various subjects related to the ISF since I got mine (silver on black). Traded an '07 RS4 for the ISF, and so far I really like it! The transmission is what sold me, and I'm really impressed with it every time I put it in manual and shift at red-line! I live in Colorado Springs, where the altitude is about 6,000'.
The point of my post is this: I recently had my ISF at Pueblo Motorsports Park for a track day, along with my '08 Cayman S which my my wife drove.
It was hot (about 91 degress) and high (Pueblo is little lower than Colo. Springs at about 5,200'), and after about 5 laps...12 minutes or so, I noticed the temp getting higher. I was having a blast, and didn't really want to shut it down, so I pushed it for another lap and a half while keeping an eye on the guage, and finally had to back off as the temp guage began flashing repeatedly. No coolant overflow or other obvious symtoms.
After a couple cool-down laps, and about a half hour parked under a tree, I went out for a few more laps, 3-4, with no problem, but the initial overheating issue has been nagging me. I know the combination of temp and altitude made for difficult conditions, but I also drove my Caymen S several times for longer periods with absolutely no overheating issues.
Anyone had a similar experience?
A few other track-related observations;
1. brakes are incredible...no signs of fading whatsoever, and they have a really nice initial bite...I know some magazines have complained about them being too "grabby" on the street, but on the track they're awsome.
2. Tranny makes you feel like an F1 pilot...both upshifting & down. Super fun, and definately quicker and less fatiqueing than a stick & clutch. The audible upshift alarm is helpful, you just wait for the beep & bang the shifter...helpful when you're driving at the limit.
3. Handling in sport mode is truly inspiring for an almost 4,000 lb car. Plus, with the trac control off, you can do some really fun sustained 2nd gear drifts...not the quick way around, but definately the fun way!
4. Tires; judging by this day of about 20 total laps (granted, some by my wife at a more sedate pace), I'd guess you could get 4-5 hard track days before they're gone.
All-in-all a very impressive sedan. There's just that nagging overheating issue. I plan to do another track day in a week or so, I'll update afterward.
In the meantime, please let me/us know if anyone else has had similar issues.
Sorry this is so long, I didn't mean to write a book.
Thanks, Bruce