Recently I've had a problem where my van will run good for about 30 minutes. But if I take it on the highway it loses it's acceleration and can't even stay up with speed limit. Actually when going down the road I can floor it and the vehicle slows down if I hold the pedal about halfway up it will continue to go about 30 MPH. Now if I hit a hill where it would need to have more power and downshift it will not ever do that. If I keep the pedal to the floor I just go slower and slower. If I pull over and put in park I can rev up the engine just fine and it always idles correctly. Have already changed fuel filter, pump
Any help would be greatlly appreciated.

 

Changed you plugs lately? Only other thing I'm thinking is a leak in a vacuum line not allowing fuel to get up there fast enough. But, I'd bet on needing new plugs and wires first. I had a little import car that acted like that, was irritating trying to merge onto I40 doing 40mph! I just knew we'd be killed!