This is the second post I heard about an ATX seeming to not engage when the gas is applied, but working almost normally when the throttle is used lightly.
My only experience with this type of problem was with an old V-8 Mercury. It turned out to be a goofy plastic clip on the linkage for the kick-down rod, which the next dealer I got to fixed for free. Does the Contour have an electronic monitoring system for the WOT downshifting, or are we dealing with a similar setup with a kick-down rod?
It's late. I should just shut up, run outside & look under the hood, and stop typing...