We fill up our 763s quite a bit during the summer to BCN. Wintertime, not so much, hence the change to the 757.

Like SoCal says, the fuel #s look fine on paper when leaving westbound. Throw in a lower than requested altitude on the NATs, delaying vectors approaching NY, a hold or two, and you get the picture. 9 times out of 10 these flights are dispatched with a re-release, meaning that the flight is only released to a certain point, and upon arrival at that point, based on actual fuel the crew and dispatch determine whether they can get "re-released" to destination.

The 757 is truly not a trans-atlantic bird, end of story.