I have this same problem and it just started about a month ago. I noticed it only happens during WOT and above 3,000 RPM. It'll bounce down about 200 or 300 RPM on the tach, but the engine doesn't miss. I did develop a rough idle though.
With that said, I have felt that it is down on top end power. Not drastically, but it is noticeable to me because I drive a decent grade on the pass during the week. My gut is telling me this is a ground issue like Joe stated, but I'm thinking more of an engine ground. I'm also going to replace my distributor because it's under warranty and I'm thinking the CPS inside it is suspect as well.
Alll little background -
Mine is a 95 4.0L 5spd. New Crank Position Sensor, distributor, coil, wires, plugs, air temp sensor, TPS, cat, new headers, new 4-port injectors, plus a few other odds and ends over the past few months to prepare for the dreaded smog test. Now that this problem developed, I'm a bit worried to try to smog it. (problem happened after the parts install, but weeks after everything was done, so I know it isn't a part swap issue)
If I figure something out, I'll let you know.