I don't think that's the cause.
You see, I've also had Advancetrack sort of flake out on me twice now. Both times was under light acceleration (The second was leaving the grocery store with a dozen eggs sitting on my passenger seat.) and both times were between 20 and 40 MPH.
It did pretty much the same thing as described. Jaming on the brakes, refusing to let me accelerate, and pulsing the application. Also the Advancetrac light on the dash was blinking like crazy.
Personally I'm leaning towards a faulty gyroscopic or wheel spin sensor myself. Unfortunately with it being an intermittent and unreproducable problem I get no help from the dealer.
Same thing happened once to me. I had to pull over and turn the car off to get it to act normal.
2011 GT/CS Race Red, 6MT, 3.55s, GT500 A/B, K&N **sold**
2014 F150 Lariat SCrew, 5.0L, 4x4