odd engine behavior

Took the Stang on it's first interstate weekend getaway this weekend. Ran about 2hours up to Canton GA, north of Atlanta. Overall, The car ran great, cruising at 80-90 in the HOV through town. Scarily enough, i was mostly running with traffic.
I had a strange thing happen twice, however. The first time I was headed up Sat, had been cruising 75-80, and downshifted to 4th to get around a slower car in traffic. After the clutch was fully engaged and I was accelating smoothly, it was like the throttle snapped closed for a split second. Even my wife noticed. I thought maybe the AC kicked on or something, but it was a significant punch, nothing the AC should have done.
Coming home yesterday, I had been running 80 coming through downtown and suddenly had to come to a near stop for a wreck. I got down in 2nd and accelated away from the initial slowdown, and it did the same thing again. Clutch was fully engaged, foot away from the pedal, and accelarting briskly, around 3500 rpm. It was a hard, splitsecond, loss of power. It happened so fast I didn't catch if the tach dropped. It was more significant than a cylinder misfire.

I haven't been able to recreate it, and it hasn't happend before.

Anybody else seen this? I got the distinct impression It might be tied to the ETC?