My Ford E150 van, when almost floored, doesn't catch gas to the engine. Then I let up, and the van slows down 5 or 10 mph the engine works fine. What could this be?

Clogged fuel filter, or it may be that the fuel pump is going bad. change filter, and while you have the line off, have a bottle ready, and put it over the line to catch the fuel. have someone turn on the key, but don't crank it, and see if you have fuel coming into the bottle. if so, then you may just have a bad fuel filter.