Failsafe mode

Similar problem:
Driving 80+ MPH for over an hour with cruise control. 85 degrees and clear.
Turned off the cruise control due to upcoming traffic, just as I stepped on the gas the car went into failsafe mode. It was quite a frightening experience until I realized what had happened. Turned the engine off, waited 1 minute, then re-started... no further problems, no codes.

I suspect Ford is using a digital signal converted from the analog temp sender unit. When electrical noise occurs just right, the computer gets the indication that the car engine is overheated. No real checks and balances from any other temperature indicating systems. (like the guage itself and the gauge backlighting which should turn red when in the overheated zone)

It was a bit scary, but no harm done.

I would contact whoever did the tune for you. IMO though the best thing you can do for your money is to have someone do a custom tune for you. Canned tunes can work fine but I think they have too much room for error since every car is different. Go to www.sctflash.com and put in your zip code and it will give you tuners in your area. I was able to get a custom dyno tune and SCT XCal2 tuner for $500 from Force Performance in Yonkers, NY. For that price it is a no brainer b/c the XCal2 alone is usually $375 so $125 for a custom dyno tune is pretty good.