Engine stutter under a load?

I have a 1999 ford contour se 2.0L 4 cylinder. Lately I've noticed once the car is warmed up (which I never drive if its not) If I put it under a load (around 4500-5500 rpms) it starts to cut out and won't accelerate as fast, then suddenly it jumps to life again and pulls hard through the redline. I'm getting no check engine light, and other than that, the car runs great. I was thinking maybe it was the fuel pump (?) I've already replaced the spark plugs, valve cover gasket, spark plug wires, alternator, and got a tune up. Not sure what else it could be. Any help would be appreciated.

Do an OBD2 code check to see what failed. I think it's a weak battery because it isn't charging up because the charging system fuse (5 amp) blew. You would be tempted to buy a new alternator. Change this burned out fuse with a 15 amp fuse and see if the battery gets charged back up.