just changed all spark plugs, yet to change wires, but still lags at 4000rpms, mostly in second gear. any idea of what the problem is?

 

3800 RPM grounding issue? Secondary injectors, maybe.

 

probably the infamous 3800 rpm hesitation. Mine had it, but it magically fixed itself. This is right when the secondary injectors kick in. Try cleaning your grounds. Do a search also as there is lots of info on this around.