Hi pgew,
My experience is that the remap certainly makes for a much smoother power curve across the rev range, but I didn't experience a lack of grunt below 4k as you describe prior to remap. Are you sure that the basics have been covered - spark plugs and coils firing consistently, no air leaks in the manifolds etc.
The remap also gives a lovely burble and pop if you request it from Mark at Z&F - especially good if you have a stainless steel aftermarket exhaust! Enjoy!