Hard to say unless you drive the thing yourself. I had a similar problem between 4000 -5000. I tried so many things, including new platinum plugs, pulled out the injectors and had them cleaned and flow tested, new oxygen sensor blah blah blah....still happening.
I swapped my old pod filter for a spanking new K&N pod..... problem solved. Guess she wasn't sucking enough air. Some times it's the little things