98 Explorer has no power

I have a 98 Explorer with the 4. L overhead valve pushrod motor it runs fine at an idle and low rpm's, but has no power at anything above 2500 rpms and will not go over 4500 even parked just reving it. On the highway the harder you push on the gas pedal the crappier it runs. It doesn't seem to miss, just has no power. I thought it was the catilitic convertor, so I tested it and its fine and not pluged. I was told that a bad throttle position sensor can make act that way too, so I switched it off another Explorer I have and it made no differance. On the Hwy it will not go over about 45 mph and takes a long time to get up to that speed. What could be the problem?

How about air filter, or fuel filter!
Have the fuel pressure checked.

Anyone else have any Ideas???? I took the air filter out and it didnt help. Fuel seams ok but I have not tested it yet.

In Park and Neutral there is a rev limiter that will prevent the engine from over revving. Since you don't indicate that the rev limiter at probably more like 3500 feels different than when driving, I suspect you have a misfire and you just don't realize it. Since you don't mention that the check engine light is on, I'm suspecting you have a vacuum leak. The leak will likely be from the PCV elbow, intake air tubing, or the intake manifold gasket. You should also consider spark plugs and spark plug wires if it's been awhile since the engine had a tune up.

-Rod